Apartment 4A

Apartment 4A is the primary setting in Big Bang Theory, and is apartment where Sheldon and Leonard live. It is situated an apartment complex at 2311 N. Los Robles. The apartment, described by Howard as Nerdvana, is full of games, action figures and everything else that he considers cool.

It is a corner apartment since there are two windows. 4A is across the hall from Penny's apartment, number 4B.

Layout
The apartment has Leonard and Sheldon's desks along the fourth wall, with a row of bookshelves along the left wall, with a small closet. The TV is also along the fourth wall, with the sofa and chairs in the middle part of the apartment. The kitchen area is on the right side of the apartment with an island (with rarely used barstools) and a large red refrigerator. There is a window in the kitchen, usually obscured by a whiteboard. The back part consists of a large window with a large additional desk near it. The apartment also has numerous whiteboards spread through it. There is a small hallway leading to the bathroom as-well as Leonard and Sheldon's rooms.There is two bedrooms in the apartment.

Bathroom
The bathroom has a double Bath/Shower. Sheldon have a shower curtain with the periodic table of elements printed on it. It also has many pictures on the walls of superheroes. Sheldon has placed a UV light box there to stop his toothbrush from being infected by germs as well as placing tape on the floor. The tape serves to avoid splatter on the mirror from flossing teeth, and to stop urine from getting on the floor when men use the toilet. Sheldon also has a squeegee to clean the mirror.

History
In The Staircase Implementation, the story of how Leonard and Sheldon meet is revealed. We find out that Sheldon had placed an ad for a room-mate after his former room-mate was driven to the brink of madness from Sheldon's antics. Leonard encounters Sheldon's former room-mate on his way to the interview with Sheldon. The room-mate tells Leonard to run away. Leonard is accepted by Sheldon as his new room-mate and inherits the former room-mate's room, only to discover that the room-mate had spray painted "DIE SHELDON DIE" on the wall.

At this time, the apartment also had significantly less funiture in the living room. Sheldon's only placement was two lawn chairs and cinder blocks in which he placed the TV. Even at this point in time, Sheldon's lawn chair was placed in the exact spot that he claims later on the couch. Their first major addition in furniture to the apartment was the leather couch, in which Leonard buys for a hundred dollars from tenants on the first floor who were moving out.

In the episode "The Bozeman Reaction", the apartment got burglarized. Some of Sheldon and Leonard's game systems were stolen. The Police were also called to the apartment in the episode "The Zarneki Incursion", in which Sheldon's World of Warcraft account was hacked.

An apartment flag is mentioned in the episode "The Staircase Implementation", and is a small blue flag with a yellow coat of arms lion on it. Flipping it up-side down signifies that the apartment is in distress.