Mensa-fied best friends and roommates Leonard and Sheldon, physicists who work at the California Institute of Technology, may be able to tell everybody more than they want to know about quantum physics, but getting through most basic social situations, especially ones involving women, totally baffles them. How lucky, then, that babe-alicious waitress/aspiring actress Penny moves in next door. Frequently seen hanging out with Leonard and Sheldon are friends and fellow Caltech scientists Wolowitz and Koothrappali. Will worlds collide? Does Einstein theorize in the woods?
Howard discovers that he can't escape his mother - even in space! Back on earth, meanwhile, Raj turns his existence as a third wheel into an art form. S6, Ep1
After learning Penny is thinking about breaking up with Leonard, Sheldon tries to intervene. Howard is being picked on in space by the astronauts. S6, Ep2
While the pressure of being in space starts to take its toll on Howard, Amy feels threatened when Sheldon hires a young female assistant, Alex. S6, Ep3
When Howard returns from space, he doesn't get the hero's welcome he expected. Meanwhile, Game Night turns into a battle of the sexes. S6, Ep4
The gang celebrates Halloween at Stuart's comic book store. Leonard and Penny discover a new spark in their relationship with a scientific seduction. S6, Ep5
Sheldon's friendship with renowned scientist Stephen Hawking is threatened by a game of 'Words with Friends.' S6, Ep6
Bernadette pressures Howard to move out of his mother's house. Sheldon finds himself caught in the middle of a fight between Amy and Wil Wheaton. S6, Ep7
Howard and Raj try to understand why Sheldon disappears every afternoon at 2:45. Leonard and Penny wrestle with jealousy in their relationship. S6, Ep8
When the University reassigns Sheldon's unused parking spot to Howard, the ensuing turf battle affects the whole gang. S6, Ep9
Sheldon plays nursemaid to a sick Amy, while Howard attempts to bond with his father-in-law on an upcoming fishing trip. S6, Ep10
Sheldon unwillingly revisits some Christmas memories during a lively game of Dungeons and Dragons, while Raj joins the girls for ladies' night out. S6, Ep11
Sheldon is accused of sexual harassment at the University and winds up dragging Leonard, Raj and Howard into the fray. S6, Ep12
Leonard's car is stolen when the guys take a road trip to a comic book convention in Bakersfield, dressed as Star Trek characters. S6, Ep13
Outraged that he's being forced to work with his university nemesis, Barry Kripke, Sheldon faces a crisis of conscience. S6, Ep14
When Sheldon and Leonard fight, it affects Penny and Amy's living arrangements. Meanwhile, Raj takes care of Mrs. Wolowitz while Howard is away. S6, Ep15
While the guys try to give their significant others the perfect Valentine's Day, Raj and Stuart throw a lonely people party at the comic book store. S6, Ep16
After a terrible date, Raj vows to never leave his apartment again. Meanwhile, Penny actually impresses Sheldon with her acting skills. S6, Ep17
Contractual Obligation Implementation. Leonard, Sheldon and Howard try to advance the cause of women in science by speaking with junior high girls about their future careers. S6, Ep18
When Howard finds a letter from his father, he's forced to confront his past. And Leonard and Penny throw a grown-up cocktail party at the apartment. S6, Ep19
Let the battle begin! Leonard, Sheldon and Raj fight for tenure at the University - and the competition heats up when the girls get involved! S6, Ep20
After one of his favourite TV shows gets cancelled too soon, Sheldon feels lost, so Amy tries to help him get over his compulsive need for closure. S6, Ep21
Leonard and Sheldon hire Professor Proton, the host of their favourite childhood TV show, to perform. Raj leaves his dog with Howard and Bernadette. S6, Ep22
When the girls' trip to Vegas falls through, the guys invite them to a Dungeons & Dragons date. Meanwhile, Raj and Lucy go on an awkward date. S6, Ep23
When Leonard is offered an exciting new job opportunity overseas, Sheldon grows jealous. Raj pushes Lucy a little too far in their relationship. S6, Ep24