Leonard and Penny

Leonard and Penny's relationship has been a major subject in the series since the beginning of season one pilot episode. Most of the involve Leonard's relationship with Penny in some way.

First Date
When Penny first met Leonard, she only thought as him as a and a  and had no romantic feelings for him at first. She asked favors of him and talked and visited him nearly every day. She ate  food with him and the others. He took Penny out for dinner in "The Fuzzy Boots Corollary"; however, Penny thought the whole gang was coming. When no one else showed up she suspected their evening was supposed to be a date. At the end of the season 1 after another bad break-up, she confessed she wanted to go out with a guy like him and with that, Leonard asked her out which she accepted. Their date went well though Penny wanted to take it slow. Afterwards, Penny gets the idea that he won't date a girl that doesn't have a college degree derailing a second date at that time.

First Relationship
At the end of Season 2, the episode "The Monopolar Expedition", Leonard and the others were arranged to go to the North Pole for three months. In that episode, she gave him a and gave him a long hug, which made Leonard concerned about leaving her. When he asked her what it meant, she said it was just a going away present. After he left and she closed the door, she whispered, "It means I wish you weren't going" revealing her hidden feelings. When Leonard returned at the beginning of Season 3, he went to see Penny and she greeted him with a passionate kiss which Leonard happily returned. Leonard gave her a preserved snowflake which she loved and they began going out again. After a quick trip to Texas to bring Sheldon home, the new couple finally consummated their relationship which they both described as weird. After realizing how weird the relationship was, they decide to return to being friends, but quickly resumed their romance within a few seconds.

Throughout season 3, they learned about each other and explored the limits of their relationship. There were some fights like Leonard belittling her for believing in psychics ("The Psychic Vortex") or Penny not telling him about her letting an ex-boyfriend stay in her apartment ("The Guitarist Amplification"), though there was a lot of make-up sex and a lot of compromises mainly by Leonard. Sheldon was often frustrated with the constant presence of Penny within his inner circle and the couple many times were treating him like they were his parents.

In the episode "The Wheaton Recurrence," Leonard told Penny he loved her, which surprised her because she wasn't ready for it, but they both got over it when they had to help Sheldon win a against Wil Wheaton in a bowling match. Wil Wheaton told Penny that it would be kinder to break-up with Leonard right away, which later was revealed to be a trick to win the bet, but Penny had already broken up with Leonard, believing it would help him.

Separated
Right after the break-up, in "The Spaghetti Catalyst" the gang "chooses sides;" Team Leonard or Team Penny. Ironically it was Sheldon who was responsible for keeping them together as friends. Penny took Sheldon to Disneyland and Penny & Leonard acted very much like divorced parents over Sheldon. Watching him sleep after they put him to bed, they decided that they could move on as friends.

In the season 3 finale "The Lunar Excitation", Penny started dating Zack and later reprimands Leonard for ruining him and destroying her ability to tolerate idiots and takes Leonard so they have sex.

In Season 4, Leonard and Penny's relationship had a bit of awkwardness. In "The Love Car Displacement", Leonard and Penny have a one-night stand and Leonard thinks they've gotten back together, but Penny says it was a one-time thing and Leonard gets upset and results in him driving fast and being followed by the police. When Leonard starts dating Raj's sister, Penny breaks down in tears, proving that she is NOT over him. Leonard's next girlfriend Priya Koothrappali wanted Leonard to stop hanging out with Penny. Penny agreed to it to help Leonard move on with his relationship. Penny hated Priya because of that and got upset with not talking to Leonard as much. At the end of Season 4, in "The Roommate Transmogrification" she admitted to Raj she regretted breaking up with Leonard, and ends up "sleeping" with Raj. Although it was revealed later in "The Skank Reflex Analysis" that they didn't actually have sex.

Second relationship (Leonard and Penny 2.0)
In "The Recombination Hypothesis", Leonard (having broken up with Priya) decided to ask Penny out on a date and envisioned a possible ending of that date. In his fantasy, things did not go well the second time around, but he decided to go ahead and ask her out anyway, and Penny agreed to go. The episode ended with Penny envisioning herself very  at a of necessity with Leonard, a possible reason for her reluctance to go out with him again and her need to pick up. She also has issues since other members of her family were pregnant when they got married. Leonard and Penny's fantasies regarding their possible reconciliation proved to have their merits when in the following episode, #101, (Season 5 Episode 14), "The Beta Test Initiation", it was shown that the two were contemplating to be official again. However, to avoid the mistakes from their first time together, they decided to take things slow by treating the relationship as a, and even went to the length of presenting each other Bug reports to settle any issues.

Things seemed to be going well by the end of the episode, with Penny kissing Leonard at his doorstep after their date and at the. In "The Friendship Contraction", it was apparent that the two are definitely in a relationship again, though they taking things slow this time around, and the beta test that was still very much going on. During a at the apartment, Leonard opted to hang out with Penny at  her apartment and the two were about to make out when Sheldon interrupted them.

In "The Launch Acceleration", Penny suggested that they move up their relationship and get ; however Leonard ruined the mood when he asked her to him while they were having sex making their relationship feel weird to Penny.

Season 6 starts with them on a date in "The Date Night Variable" where a lonely Raj crashes their date and insists that Penny tell Leonard that she loves him. Leonard wants to talk about their relationship; however she has had a hard day and wants to just hang out together. Penny is expressing doubts about her feelings for Leonard, though she claims to be happy with the relationship in "The Decoupling Fluctuation". She almost tells Leonard about her doubts and then ends up after looking into his sad eyes. In "The Higgs Boson Observation", Penny while spying with Amy sees Sheldon's pretty new Alex Jensen flirting with Leonard who is not responding. Later when Sheldon and Alex enter the apartment, Penny tells her about Leonard and their five year experiment together (relationship) and then she leads him off to her apartment for sex. In the theme episode "The Holographic Excitation", Penny gets advice from Bernadette that you get out of a relationship what you put into it and that maybe Penny should get more interested in Leonard's work (it is also revealed that, up until this point, Penny's view of their relationship had been one-sided in her favor). She visits his lab and is wowed by his images and says that she sometimes forgets how smart he is. Penny heats up their relationship by starting to engage in sex in different locations, twice in his lab and twice in the photo booth at the Halloween party.

In the episode "The 43 Peculiarity", Penny is working on a class oral project with an student, Cole, who makes Leonard. Leonard follows Cole down the stairs warning him about Penny's boyfriend, the " leader". Penny witnesses his deception and gets mad at Leonard telling him that he has nothing to worry about because she chooses to be with him and that he knows that she loves him. This pronouncement shocks both of them since Penny has never told Leonard that she loves him and she runs off scared before she breaks into tears. At the same time, Sheldon's assistant Alex Jensen is starting to hit on Leonard though he doesn't recognize her intentions. In "The Egg Salad Equivalency", Alex asks Leonard out to after he expresses an interest in the Physics lecture she is going to and this attention really startles Leonard. Though it makes him feel good "to the bones" to have an attractive young woman interested in him, he tells everyone he still loves Penny and wouldn't do anything about it. He mentions Alex's actions to Sheldon who tries to talk to her about it and lands the whole gang in the Human Resources Administrator's office. He also didn't tell Penny about Alex's actions which made her feel really insecure about their relationship. Leonard apologizes by showing up at her door playing a little ditty on his.

In "The Spoiler Alert Segmentation", Leonard suggests that he move in with Penny after he again gets exasperated (again) with Sheldon. He asks her if she's all right with it, but she only agrees not to hurt his feelings and even tells Sheldon. She does try to get him admit that Sheldon can't get along without him. Amy plans to move in with Sheldon as roommates. When Amy confronts Penny since she can't move in with Sheldon, Leonard overhears the conversation. Penny tells him that he never asked her if she was ready. Then Amy and Penny go off to and talk about their jerky s and Leonard ends up back in Apartment 4A. Amy also scares Penny when in anger says that she and Penny should move in together. In "The Tangible Affection Proof", Leonard takes Penny out to dinner for. Penny feels that all the efforts never meet the expectations and she will end up disappointed. At dinner, Penny sees an old boyfriend proposing to the girl that broke them up. Leonard again tries to propose and Penny stops him. They begin to argue in front of Howard and Bernadette who have their own issues that night. After they barely say good night, Leonard tells Penny that she ruined the whole evening. Penny finally admits that she has issues. She is so happy right now that she knows they are going to get married and since that relationship is forever that scares her. Leonard then puts the responsibility of proposing on her and that she should do it when she's ready. In the end, she does ask him to be her valentine.

In "The Closure Alternative", Penny was concerned about the passion Leonard showed for, s, and various while she had no passion in her life. Her dreams had always been to become a famous and live a glamorous life. Anything less than that she felt was settling. Her came that she is passionate about her boyfriend Leonard and all her wonderful friends.

In "The Bon Voyage Reaction", Leonard takes a job working on a Stephen Hawking expedition in the for four months over the summer. Penny will miss him, but knows that it is a good opportunity and sends him off. At the, she is fussing over him like a sending her  off on a business trip. She also has to watch Sheldon over the summer, too.

In "The Hofstadter Insufficiency", Leonard hurts Penny because he seems to be having such a great time on the ship, she thinks that he is not even missing her. In "The Deception Verification", Leonard makes up for it by showing up early and hides in her apartment so that they can spend time together a couple before telling the gang that he's back. It works until Amy and Sheldon find them together after they think that Penny is cheating on Leonard.

In "The Raiders Minimization", Penny purchases a psychology book that Beverly Hofstadter has written about all his problems growing up for a night school class. Leonard finds out that Penny will do things he wants to do [ditch going to a sports bar, watch geeky shows, and have sex] and uses her. Leonard mentions it to Howard, who fails to try it with Bernadette, so his actions make it back to Penny. She dresses up for sex tempting him and then for revenge makes him Skype with his mother to discuss his actions much to Leonard's disgust.

In "The Romance Resonance", Howard makes a romantic gesture to Bernadette by writing her a song. Leonard mentions that Penny never does anything like that, except for sex which doesn't count. Penny is determined to romance Leonard. Raj can only suggest that she cook for him or reenact a scene from a romantic movie. Finally after a candlelight dinner, Penny puts on some romantic music, spreads rose petals into her neatly cleaned bedroom and presents Leonard with a first edition of his favorite book from when he was growing up,. Unfortunately, Leonard had already purchased the book after they had seen it in a used bookstore together. Penny gets upset telling him about all the thoughtful things he had done for her and shows him her collection. An airplane ticket, a rose given to her "just because" and the eleven page letter he wrote her after the first time they slept together. Leonard was very touched that she kept all these things. He then kisses her, showing that Penny did do something romantic.

In "The Thanksgiving Decoupling", Penny reminisces about a Thanksgiving she had in with former boyfriend Zack Johnson which included one of those "silly fake weddings". Penny appears devastated when her friends inform her that the wedding was real and she is Mrs. Zack Johnson. Penny and Leonard argue about how quickly she should get her annulment so Penny invites Zack over to their Thanksgiving dinner at Howard's mother. Zack appears as dimwitted as ever telling them that breaking up can be hard on the kids which they don't have. Finally, Penny and Leonard make up and she tells him that the next time she gets married it will be for real, for love (jokingly) or for money.

In "The Hesitation Ramification" and "The Occupation Recalibration", Penny gets a part in the TV series NCIS and is very disappointed when her scene is cut and not aired. Frustrated and tipsy, she sees her life crumbling when Leonard reminds her that she still has him. She agrees with him and probably to show some advancement in her life, she kneels down and proposes to him. All Leonard can utter is "Umm", much like when he wouldn't succumb to her drunken advances after her Halloween party in "The Middle Earth Paradigm". Penny gets very upset since she doesn't think he wants to marry her. After she storms out, Leonard is afraid to ask her if their relationship is now over. The next day/episode he does visit Penny who assures him that they are still together and that he did the right thing not agreeing to her proposal because she was a mess. Now she has rethought her career and decides to quit the Cheesecake Factory and focus all of her time on acting. Leonard does support her though he is obviously worried about her.

In "The Table Polarization", the gang wants to add a dining room table to Apartment 4A which Sheldon objects to. Penny gets Leonard to pick out a dining set that she likes and gets Leonard to stand up more against Sheldon. Sheldon objects to Penny changing Leonard to stand up against him. Penny points out that Amy has changed Sheldon who agrees and then decides to break up with Amy.

In "The Friendship Turbulence", Penny, despite what Leonard is telling her, is reluctant in her acting abilities; he still encourages her to keep trying. When her car finally breaks down after years of the "Check Engine" light blinking, Leonard gives Penny a new car so that she won't have to get her job at the Cheesecake Factory back to pay for repairs. Penny is touched by the gesture and immediately hugs Leonard.

In "The Mommy Observation", Raj has a murder mystery night where they speculate where they will be twenty years in the future. The couple starts thinking about how they will deal with each other's success. Penny figures that Leonard will follow her around if she is famous and making a lot of money while Leonard thinks that he might be tenured at a university and can move around. Finally Stuart ends the argument saying that he thinks that they have the strongest relationship he knows. Penny brought Leonard out of his shell and Leonard got Penny thinking about her place in the bigger picture.

In "The Gorilla Dissolution", Leonard and Penny get back in her apartment after getting fired from her movie. Penny wants to start making smarter decisions about her life. She says that they could get married and Leonard asks her to be serious. Leonard wonders if he is a smart decision, like choosing a healthy boring bran muffin. Penny doesn't care what pastry he is because she is CHOOSING HIM. Leonard is still talking about being a pastry like a Cinnabon or a Strawberry Pop Tart something that she is excited about. Penny tells him to forget about it. Leonard does want to marry her, but feels that she is just feeling sorry for herself because she was fired. Penny explains that it may seem that way, but getting fired made her think that fame and fortune is not what is going make her happy. Leonard wants to know what will make her happy. "You, you stupid Pop Tart!" she yells at him. Leonard finally says that he guesses that he is in, which also bothers Penny. Leonard then retorts that it is an excited "I guess I'm in" and they agree that they are engaged which still seems somewhat anti-climactic. To change the mood, Leonard pulls a diamond ring out of his wallet that he has had for a couple of years, gets down on one knee and asks Penny formally. Penny says "Oh my God, yes!" He slips the ring on her finger that still has ape hair glued to it and they embrace.

In "The Status Quo Combustion", Leonard and Penny announce their engagement; however, the gang is more excited about Raj and Emily hooking up. Leonard goes searching for the missing Sheldon and finds him at the railroad station leaving time to think about all the changes in his life. Leonard wants him to come home, but Penny convinces him that he should let Sheldon go.

Engagement
In "The First Pitch Insufficiency", they go on a double-date with Shamy where Sheldon is bragging about their relationship is so much better than theirs. Shamy has an 8.2 out of ten for relationship stability based upon well proven criteria. Leonard looks at it; however, Penny doesn't want to take the test. She already has his doubt and doesn't need them confirmed. They are engaged and still have very little in common which scares her. It also scares Leonard, but he still want to face all their problems together. His reassure really touches Penny and Amy who would like Sheldon to say things like that. Penny's fear of getting married and being pregnant from "The Recombination Hypothesis, is revisited as she wants to prove to her family that she is not getting married due to a pregnancy like her sister.

In "The Hook-up Reverberation", Raj tells the gang that Stuart didn't get enough insurance money to reopen his store. The guys decide to give him the money and were enthusiastic about owning a comic book store. Leonard talks to Penny who wonders why they should even be talking about finances. Leonard say that they are getting married. Then Penny wonders if mounds of  debt will affect them financially. What is her current financial position?

Finances would later be a concern in "The Expedition Approximation". Penny sells the car after getting one from the Zangen, and gives the money to Leonard. However, he insists that she keep the money since the car was a gift, and he really doesn't need it. After exchanging the money back and forth, they go to Howard and Bernadette for advice on how to deal with finances. This doesn't work well as Bernadette and Howard get into a heated argument over Bernadette making more money, and Howard making unnecessary purchases. During the visit, Penny and Leonard both agree that they should use the Wolowitzes' situation as an example of what not to do in the future, so that money doesn't get in the way of their love. Even though Penny is concerned about how Leonard will feel when she starts making more money than him, he assures her that things will be okay, given that his mother used to emasculate his father at everything, especially through finances, considering she makes/made more than him. Later, they decide to have sex on the money put into a pile on their bed.

In "The Prom Equivalency", Amy and Bernadette throw a do-over prom on the roof of the apartment building. Penny is at first reluctant to attend the party because they always disappoint her, but Leonard tells her that he really wants to take the most beautiful girl to the prom, this time. She wears her old red prom dress. The roof is decorated wonderfully and Penny really gets into the mood. While others are still getting there, Penny and Leonard dance alone without any music on the roof. First they conclude that they probably would not have approached each other if they had been at the same prom. They are both definitely in a romantic mood, while Penny is also glad they aren't having the drama normally seen at proms.

In "The Space Probe Disintegration", Leonard tells Sheldon that his attitude is why he and Penny are not living together. After a tearful period thinking about them him moving out, Sheldon let's him go one night a week to stay at Penny's. Sheldon still sleeps on her couch that night. Leonard and Penny are finally living together once a week.

In "The Colonization Application", Leonard goes to the dirty book store and gets a sex painting kit, where they cover themselves in body paint and have sex on a canvas. Not satisfied with their first try, they do it again to prove that they are not a boring couple. Happy with the next one, Penny will not hang it in her apartment, but plans to give it to Sheldon and tell him that painted it.

In "The Fortification Implementation", Leonard and Penny appear on Wil Wheaton's for him and Penny to talk about and take calls about their horrible ape movie. Actor/director calls in and is a big fan of the movie and he loved Penny's performance. He wants Penny to audition for his new movie "". Leonard reminds her that she already has a. Penny and Leonard have an intense discussion about her. Penny reminds him that they could have a wonderful if she becomes  and. Leonard is just trying to protect her after all her other disappointments. Penny just wants him to be happy for her. He was happy for her when she got her current job that pays a decent. Decent? She makes twice what Leonard makes. Penny has been putting together a diversified of stocks and bonds with her broker. Leonard says he doesn't because he doesn't have any. Leonard wonders who the mature one now in this relationship is. Penny asks him if he would feel better if she did something stupid like sneaking out from work and trying out for a Kevin Smith movie. Leonard agrees and Wil Wheaton comments that Penny just played him like a.

In "The Graduation Transmission", Leonard plans on taking Penny with him to his hometown to watch him give a commencement speech at his high school. However, a big storm in the East Coast cancels their plans. To make him feel better, Penny sleeps with him, makes him pancakes for breakfast, and buys him a graduation cap and gown, revealing that she convinced the school to let him give his speech over Skype. After the ceremony is done and the speech is over, Penny comments on how Leonard's speech was the best she's ever heard.



In "The Commitment Determination", Sheldon keeps pushing them for a wedding date. The couple insists that they aren't in a hurry, are in a good place emotionally and are concentrating on their careers. Thinking about the wedding details they decide on a small church wedding dressed in black tie tuxes and no releasing of butterflies. Suddenly Penny smiles and sits close to Leonard. She tells him that she's free that night. They could go to Vegas and just get married. Leonard agrees. Sheldon is happy for them, but still doesn't want them to sit in his spot. Driving to Vegas, Penny is very happy and glad that they took their time to get to know each other. No surprises and no regrets. Leonard has on regret where he was drunk and made out with a woman on his North Sea expedition. Penny was not happy, but still wants to marry him. They were last seen still heading to Vegas to a wedding chapel.

Marriage
In "The Matrimonial Momentum", Penny and Leonard finally do get married in a little ceremony in a Las Vegas wedding chapel. Leonard tells Penny, "Penny, we are made of particles that have existed since the universe began. I like to think those atoms have traveled 14 billion years through time and space to create us so that we could be together and make each other whole." Penny is very touched and due to them being best friends, she quotes the song "You got a friend in me" to Leonard. Leonard carries Penny across the threshold and everything seems OK until they start to kiss. Penny can't help but think about Leonard with the other girl. Leonard tries to downplay the experience. He says he feels guilty every time he sees her. Penny finding out that he works with her and sees her on a regular basis is not happy at all. The last scene of them together is both of them arguing as they come up the stairs of the apartment building and they each go into their own apartments. In "The Separation Oscillation", Leonard has a nightmare that Penny got even with him by making out with Sheldon. This spurs Leonard to try to make things right. He finally confronts Mandy, his kissing buddy from the North Sea, about the incident and it doesn't seem to mean much to her. Leonard also realizes that he really was trying to sabotage the relationship. He went and talked with Penny and tells her. She too realizes the she has been trying to sabotage their relationship. Leonard then confesses, "I've loved you from the moment we met and I will keep loving you until the end of time." Penny is very touched and tells him that that was the most beautiful thing anyone has ever said to her. He follows with getting down on one knee and asks, "Penny Hofstadter, will you please stay married to me?" She replies "Aw, damn it, you topped it." and they kiss. They head into the bedroom to formalize their marriage. Later Sheldon gives them a wedding present - a trip to San Francisco for the three of them. Sheldon does think he's in their relationship.

In "The 2003 Approximation", Leonard finally moves out of his apartment and eventually moves in with Penny into her apartment. The sleeping arrangements are still a little complicated. Even though they are living together in 4B, they sometimes sleep in 4A, in Leonard's old room. This is due to Penny having a change of heart at the last minute after feeling sorry for Sheldon who was having a hard time dealing with his breakup with Amy and Leonard moving out.

In "The Helium Insufficiency" it is also apparent that Leonard is still maintaining an office in 4A.

In "The Sales Call Sublimation", Penny convinces Leonard to visit a psychiatrist so that she can give her a sales pitch for her meds. Both end up talking to her discussing their insecurities. Leonard seems out from under his mother's influence and wants to do things without worrying able how his mother judges him. Penny is told that she might be replacing his mother because Leonard is turning her into her, which is not true.

In "The Valentino Submergence", Leonard and Penny go out to dinner for Valentine's Say and have to wait for an hour and suffer through an unsympathetic maitre D'. Penny decides to flirt with her, gets nowhere and get called "ma'am". She tries to get him to acknowledge that they are almost the same age; however, he is 21 and she is 31. Next she drags Leonard out of the restaurant "while she is still young". After a fast food meal in the car, they look for something young and fun to do. The "Moulin Rouge" movie is too late, no skinny dipping or dancing either. They end up dressed as cupids breaking in on Sheldon's "Fun with Flags" programs yelling "Happy Valentine's Day" and that they are "young and fun".

In "The Positive Negative Reaction", they discuss having children one day. Penny says she is not in a rush, but someday they can. Leonard adds that he thinks they would make amazing parents.

In "The Solder Excursion Diversion", Penny and Bernadette help out Leonard and Howard with their project. When the men leave to get more solder, they get sidetracked with a special screening of Suicide Squad. Raj rats them out to the girls after he finds out and they decide to get revenge, but it isn't necessary as the men returned apologizing with flowers and the offer to take them out to dinner.

In "The Big Bear Precipitation", Sheldon spills the secret about Leonard's bank account, making Penny angry. She and Leonard get into an argument after he brings up her credit card debt. When discussing the situation, Penny explains that she's also been keeping a secret from Leonard; she hasn't been happy about her job having to flirt to get her sales; however, she will keep at it because it is the responsible thing to do.

In "The Viewing Party Combustion", Leonard and Sheldon fight about having a Roommate Agreement meeting and Penny takes Sheldon's side due to her sibling feelings for him. Amy tells Leonard she's sometimes annoyed at the closeness of their significant others and reveals to him that she uses him and has him add things to the Roommate Agreement to get her way and not fight with Leonard. Leonard becomes mad and he and Amy confront Penny and reprimand her for always defending Sheldon, but in the end everyone reconciles.

In "The Line Substitution Solution", Penny agrees to spend some time with Leonard's mother, Beverly so that they can have a stable relationship. It's revealed that Beverly only had trouble getting along with Penny due to being upset about not knowing about the wedding, so they decide on having another ceremony for everyone being involved with it. Later that night in "The Convergence Convergence", she tells Leonard about the idea of the redo ceremony, and that they can include their friends and family this time. Leonard agrees to this, and they also decide to invite his father.

In "The Conjugal Conjecture"; the actual ceremony is officiated by Bernadette. Penny tells him how much she loves him and how glad they did elope. Leonard just tells her how much he loves her and that he can't believe she is with him. Also that he doesn't care if he knows why.

In "The Cohabitation Experimentation", Sheldon and Amy move into Penny's apartment for a five-week cohabitation experiment after Amy's apartment suffers a plumbing problem. The Hofstadters are so excited about finally having a place of their own that they put on music (which Sheldon would never let them do) and have a private dance party in their underwear.

In "The Fetal Kick Catalyst", Penny is signing autographs for fans of the Serial Ape-ist movies where the fans think that she is a terrible actress and can't believe that the nerd Leonard is her husband. The fans sit around Leonard as he tells his story how he won the hot actress.

Trivia

 * Interestingly, this is the only major (and current) relationship on the show that was not set up by someone else or a third party. Howard and Bernadette were set up by Penny, Sheldon and Amy were set up by Howard and Raj, who posted Sheldon's information on a dating site and set up a date, and Raj and Emily met through online dating.
 * Whole relationship started with Leonard's infatuation with Penny followed by her appreciation of how loyal, faithful and what great guy he is. Being that cute and that smart also turns her on. He tested her vision of his faithfulness when he did make out with another girl on his research ship expedition, though it didn't mean anything to the woman.
 * This is also the only relationship that has broken up more than once. (The Valentino Submergence)
 * At various points in the series, each of the guys (save for Stuart, who served as the "tool" to improve their relationship) have acted as Leonard and Penny's "third wheel". Howard spent his time with the couple when Raj started working for Sheldon to keep his visa valid ("The Pirate Solution"), Raj spent his night with them when Leonard wanted to talk to Penny about their issues ("The Date Night Variable") and he also interrupted their one-night stand ("The Love Car Displacement"), and Sheldon puts himself into their relationship constantly, even going so far as to behaving like he was their child, and worming his way into their marriage after his breakup with Amy ("The Separation Oscillation", "The 2003 Approximation"), or calling their relationship "Our Marriage".
 * Interestingly, it was through the machinations of Leonard and Penny's relationship that Howard was made into a better man; If Leonard hadn't told Penny about his girlfriend pact with Howard and if Penny never said 'yes' and chosen Bernadette, Howard and Bernadette wouldn't have met and bonded over their dislike of their overprotective mothers and then... Howard would still be alone and a creepy pervert. And who knows how long it would've been before he was reformed?
 * Leonard admits in "The Fetal Kick Catalyst" to a previously unknown proposal to Penny that was written by a sky writer; however, Penny didn't look up and missed it.

Quotes
The scene of Leonard and Penny's wedding


 * Minister: Before I go any further, have either of you prepared your own vows.
 * Penny: No.
 * Leonard: Yes.
 * Penny: You wrote vows?
 * Leonard: Yeah.
 * Penny: Well, I don’t have any. You’re kind of making me look bad.
 * Leonard: It's okay. I don’t have to say them.
 * Penny: I’ll come up with something mushy. You’ll cry. We got this.
 * Leonard: Penny, we are made of particles that have existed since the universe began. I like to think those atoms have traveled 14 billion years through time and space to create us so that we could be together and make each other whole.
 * Penny: Wow.
 * Minister: Penny.
 * Penny: Right..um..okay. Leonard, I mean, you’re not only the love of my life. I mean, you’re my best friend. You’ve got a friend in me. You got troubles. I got them, too. There isn’t anything I wouldn’t do for you. We stick together, and we can see it though…cause you got a friend in me.
 * Minister: Isn’t that the song from “Toy Story”?
 * Penny: He loves that movie.
 * Leonard: (crying) I do.

The Wedding Decision:


 * Penny: Um, I’m free tonight.
 * Leonard: Are you saying you want to get married?
 * Penny: Vegas isn’t that far away.
 * Leonard: I’m in. Let’s do it.
 * (Penny squeals)
 * Sheldon: After all these years. I’m really happy for the two of you.
 * Penny: Oh, thank you.
 * Leonard: Thanks.
 * Sheldon: Now get out of my spot.

The Engagement:


 * Penny: Oh, my God. What a day.
 * Leonard: Can I get you anything?
 * Penny: No. I need to start making some smart decisions.
 * Leonard: With your career?
 * Penny: With my life.
 * Leonard: Like what?
 * Penny: I don’t know. We could get married.
 * Leonard: Come on, be serious.
 * Penny: I am.
 * Leonard: Why? Because I’m a, a smart decision?
 * Penny: Well, yeah.
 * Leonard: So I’m like a bran muffin.
 * Penny: What? No, that’s not what I’m saying.
 * Leonard: No, it’s exactly what you’re saying. I’m the boring thing you’re choosing because I’m good for you.
 * Penny: What does it matter? The point is, I’m choosing you.
 * Leonard: Well, it matters a lot. I don’t want to be a bran muffin. I, I want to be a Cinnabon, you know? A strawberry Pop-Tart. Something you’re excited about even though it could give you diabetes.
 * Penny: Sweetie, you can be any pastry you want.
 * Leonard: No, no. No, it’s too late. I’m your bran muffin. Probably fat-free and good for your colon.
 * Penny: You know what? Forget it. I never should’ve brought it up.
 * Leonard: You know I want to marry you, but you’re only doing this because you got fired and you’re feeling sorry for yourself.
 * Penny: Okay, it may look that way, but getting fired from that movie was the best thing that could have happened to me, okay? I finally realize I don’t need to be famous or have some big career to be happy.
 * Leonard: Then what do you need?
 * Penny: You, you stupid Pop-Tart.
 * Leonard: Oh. Then I guess I’m in.
 * Penny: Really? You guess you’re in?
 * Leonard: Not like, I guess I’m in. Like I guess, I’m in!
 * Penny: Okay.
 * Leonard: Cool.
 * Leonard: So is that it? Are, are we engaged?
 * Penny: Yeah, I think so.
 * Leonard: All right.
 * Penny: What’s wrong?
 * Leonard: I’m not sure. Just feels a little anticlimactic.
 * Penny: Yeah, it kind of does, huh?
 * Leonard: Oh, I know. This might help.
 * Penny: Where did you get a ring?
 * Leonard: I’ve had it for a couple years, not important. Penny, will you marry me?
 * Penny: Oh, my God, yes.
 * Leonard: This would have been so much more romantic if you didn’t have monkey hair on your finger.

Leonard's "I love you, Penny" Confession:


 * Penny: Having a little trouble catching your breath there?
 * Leonard: No, no, I’m good. If my P.E. teachers had told me this is what I was training for I would have tried a lot harder.
 * Penny: Do or do not. There is no try.
 * Leonard: Did you just quote Star Wars?
 * Penny: I believe I quoted Empire Strikes Back.
 * Leonard: Oh, my God. I’m lying in bed with a beautiful woman who can quote Yoda. I love you, Penny.
 * Penny: Oh. Oh. Thank you.
 * Leonard: You’re welcome. I just wanted to put that out there.
 * Penny: Oh, yeah, no, I, I’m, I’m glad.
 * Leonard: Good. Glad is good.
 * Penny: Yeah. Yeah. No, no. Um. So, it’s getting pretty late. We should probably go to sleep.
 * Leonard: Yeah.
 * Penny: Okay.
 * Leonard: Yeah.
 * Penny: Hmm.
 * Leonard: Yeah, probably.
 * Penny: Okay, good night, sweetie.
 * Leonard: Good night. (Penny looks shocked.)

Third Season Breakup:


 * Penny: Leonard, stop pressuring me.
 * Leonard: I’m not pressuring you.
 * Penny: Yeah, you are! Just back off!
 * Leonard: Okay, I’m sorry. I’ll shut up.
 * Penny: I didn't mean shut up.
 * Leonard: Fine. Just tell me what to do, and I’ll do it.
 * Penny: No, this isn't fair to you, Leonard. I’m sorry.
 * Sheldon: Wait! Where are you going? Penny, come back! I’ll get you ice cream!
 * Leonard: No, let her go.
 * Sheldon: Are you insane? If she leaves, it’s over!
 * Leonard: I’m pretty sure it’s already over.

Penny's "I Love You" Confession


 * Leonard: Hi.
 * Penny: Hey. Shouldn't you be out with your gang spray-painting equations on the side of buildings?
 * Leonard: Come on, I’m sorry.
 * Penny: I just can’t believe you don’t trust me.
 * Leonard: I feel... Of course I do.
 * Penny: Then why did you embarrass me in front of my friend who, by the way, knew exactly who you were?!
 * Leonard: Really?
 * Penny: Your picture’s on my refrigerator!
 * Leonard: Oh. You know, I’m really starting to not like this guy.
 * Penny: What is your problem? Do you use up all your thinking at work and then have none left over for when you get home?
 * Leonard: I don’t know. It’s hard sometimes. Everywhere you go guys hit on you, even if I’m standing right there. And they are all taller than me. Why is everyone always taller than me?! You know what? This is all in my head. It’s my problem, not yours.
 * Penny: Leonard. Why do you always do this? Listen to me. You are the one I’m with. You know I love you. So would you please relax--because you are driving me crazy!
 * Leonard: You know that’s the first time you ever said that you love me.
 * Penny: Yeah...
 * Leonard: Are we supposed to pretend it’s not a big deal?
 * Penny: That’s exactly what we’re going to do... because you’re about to make me cry and we both know that if I start crying, you’re going to start crying.
 * Leonard: You’re right, you should go.
 * Penny: Fine! [Runs away downstairs]

Third Season Hookup:


 * Penny: Leonard, you’re back.
 * Leonard: Yeah, I just stopped by to say… (She grabs him and kisses him passionately.) Yeah, so, hi!
 * Penny: Hi! (They stumble, kissing, into her apartment and slam the door shut.)
 * Howard: Dammit, I should have gone over and told her we were back.
 * Raj: (Sarcastically) Yeah, it was first come, first served.

Arctic Farewell:


 * Penny: Oh, Leonard, what time is it?
 * Leonard: Its 7 a.m. I’m sorry it’s early, but we’re leaving soon, and I needed to talk to you.
 * Penny: Okay.
 * Leonard: What did you mean when you said you’re going to miss me?
 * Penny: Um, I don’t know. You’ll be gone and I’ll notice.
 * Leonard: (indicating the blanket) Okay, well, um, what about this? What does this mean?
 * Penny: Wine, credit card and late night television are a bad combination.
 * Leonard: All right, fine. What about that really long hug? What did that mean?
 * Penny: That wasn't a long hug.
 * Leonard: It was at least five Mississippi’s. A standard hug is two Mississippi’s tops.
 * Penny: Leonard, I don’t know what to tell you. It was just a hug.
 * Leonard: Glad we cleared that up.
 * Penny: Yeah.
 * Leonard: I guess I’ll see you.
 * Penny: Okay, have a safe trip.
 * Leonard: Thank you. Bye.
 * Penny: Okay, bye. (Penny closes door. Says to herself) It means I wish you weren’t going.

Leonard Asks Penny Out:


 * Penny: I swear to God, I am done with guys like that. You know, macho, with the perfect body and the hair, and the money.
 * Leonard: Yeah, that must get old quick.
 * Penny: You know, just once, I would like to go out with someone who is nice, and honest, and who actually cares about me.
 * Leonard: What about me?
 * Penny: What about you what?
 * Leonard: What about if you went out with me?
 * Penny: Are you asking me out?
 * Leonard: Um… yes… I am… asking you out.
 * Penny: Wow.
 * Leonard: I was just going off your comment about the nice guy…
 * Penny: No, I know, I got that. Yeah, totally.
 * Leonard: (continuing through Penny): …thing and honest but, it’s no big deal…
 * Penny: Yes.
 * Leonard: Yes what?
 * Penny: Yes, I will go out with you.
 * Leonard: Really?
 * Penny: Yeah. Why not, I mean, what do I have to lose?
 * Leonard: Yeah. That’s the spirit.

Leonard and Penny's First Date:


 * Penny: Hi.
 * Leonard: Hi.
 * Penny: come on in.
 * Leonard: Thank you. You look very nice.
 * Penny: Thank you. So do you.
 * Leonard: I made an eight o’clock reservation.
 * Penny: Okay, great, listen, um, maybe we should talk first.
 * Leonard: Oh. Okay. But before you say anything, have you ever heard of Schrodinger’s Cat?
 * Penny: Actually, I’ve heard far too much about Schrodinger’s Cat.
 * Leonard: Good. (He grabs her and kisses her.)
 * Penny: Alright, the cat’s alive, let’s go to dinner.

Leonard and Penny's First Breakup:


 * Penny (opening door): Hi.
 * Leonard: Yeah, hi, listen, I know what’s been bothering you about us, and I have the answer.
 * Penny: What are you talking about?
 * Leonard: First I want to say that it’s not Sheldon’s fault, he tried very hard to keep your secret, if Howard hadn't drugged him he would have taken it to his grave.
 * Penny: He told you?
 * Leonard: Yes, but it's okay. Now that we know what the problem is, there’s a simple solution. (Hands her a brochure.)
 * Penny: Pasadena City College?
 * Leonard: A place for fun, a place for knowledge. See, this man here’s playing hacky sack, and this girl’s going to be a paralegal.
 * Penny: Wow, I get it, because Dr. Leonard Hofstadter can’t date a girl without a fancy college degree.
 * Leonard: Well, it’s really not that fancy, it’s just a city college.
 * Penny: Right, but I have to have some sort of degree to date you?
 * Leonard: That doesn't matter to me at all.
 * Penny: So, it’s fine with you if I’m not smart.
 * Leonard: Absolutely. (She slams the door in his face.) Okay, this time I know where I went wrong. (Looking up and seeing the camera) Oh, bite me!

Leonard and Penny's Second Wedding


 * Stuart: Nice to see you again Dr. Hofstadter. I’m uh, Leonard’s friend Stuart.
 * Beverly Hofstadter: Nice to see you, too.
 * Alfred Hofstadter: Oh, I’m Alfred, Leonard’s father.
 * Stuart: Oh. Oh, hi. Uh. I’m sorry. Did you like to sit together?
 * Together: No.
 * Stuart: I was wondering why the first row was available.
 * Bernadette: Okay, I think we’re ready.
 * Amy: {Playing Wagner’s Bridal Chorus on her harp. Penny enters on her Dad’s arm.}
 * Sheldon: Why do people cry at weddings?
 * Mary Cooper: They’re practicing for what's coming later.
 * Susan: Thank you for cleaning yourself up for your sister’s wedding.
 * Randall: And thank you for my new teeth.
 * Wyatt: Welcome to the family, Leonard. Don’t lend your new brother-in-law money.
 * Bernadette: We’re here today to celebrate love.
 * Beverly Hofstadter: Sigh.
 * Alfred Hofstadter:: Sigh louder. No one heard you.
 * Stuart: Really. I can move.
 * Bernadette: Not just Leonard and Penny’s love, but the love for them as well as each other.
 * Sheldon: Speaking of love. STD’s among the elderly are sky-rocketing.
 * Bernadette: Love is patient, but it’s not going to put up with all the side-chatter. So let’s knock it off.
 * Howard: At least she’s yelling at someone else for a change.
 * Bernadette: Howard!
 * Penny: Okay, I understand everyone’s a little tense today, so I’m just gonna get to the important stuff. Leonard standing here with you in front of our family and friends is bringing up a lot of feelings. Like what a good idea it was to elope the first time. But also how incredibly happy you make me. Thank you for marrying me. Hopefully for the last time.
 * Leonard: Penny…as a scientist, my job is to figure out why things happen. But I don’t think I’ll ever understand how someone like me could get to be with someone like you. You know…maybe…I don’t need to understand it, I just need to be grateful. I love you Penny.
 * Penny: Oh.
 * Bernadette: Anybody have anything snarky to say about that? Didn’t think so.
 * Alfred Hofstadter: I’d like to say something. Beverly, I know that we don’t bring out the best in each other. But something wonderful did come out of our relationship: that young man right there.
 * Beverly Hofstadter: I couldn’t agree more.
 * Stuart: That’s beautiful.
 * Bernadette: Thank you. All right, let’s continue.
 * Sheldon: Yeah, excuse me. I need to say something to someone pretty special. I just can’t wait any longer.
 * Amy: It’s happening.
 * Sheldon: Leonard. You and I have had our ups and downs. But I have always considered you my family. Even before the recent threat of our parents fornicating like wrinkly old rabbits. I don’t always show it, but you are of great importance to me. Both of you.
 * Penny: Oh.
 * Leonard: Thank you.
 * Bernadette: Okay. I now pronounce you husband and wife. And the weird other husband that comes with the apartment.