Leonard keeps an affair a secret from Sheldon, Howard and Raj.
Leonard keeps an affair a secret from Sheldon, Howard and Raj.
Sheldon's answers during an FBI interview put Wolowitz's security clearance in jeopardy.
While the guys camp in line for a long-awaited movie screening, Penny and Bernadette invite Amy to her first slumber party.
Penny asks Leonard to lie to her father, while Howard, Raj and Bernadette pull an all-nighter at a telescope.
Amy finds she has sexual feelings for Penny's ex, while Koothrappali and Wolowitz try to prove who would be the better superhero.
The guys find a "super" use for Penny's new boyfriend, Zack, when they enter a costume contest as the Justice League.
Leonard's idea for a smartphone app derails his friendship with Sheldon.
Bernadette runs into her ex-boyfriend while attending a science event with Wolowitz.
Hoping it will make him a better teacher, Sheldon has Penny give him acting lessons. Raj has fantasies about a friend's girlfriend.
A wealthy donor to the university makes Leonard consider how far he's willing to go for the sake of science.
As Wolowitz contemplates taking things with Bernadette to the next level, Leonard rekindles his relationship with Raj's sister.
Sheldon becomes concerned when everybody begins to hang out at Raj's apartment and discovers Leonard is the center of the group.
Sheldon is baffled by Wolowitz's magic trick. Meanwhile, Leonard realizes dating Priya may make it impossible to continue being friends with Penny.
Sheldon's World of Warcraft online game account is hacked and he is determined to find out who did it. Also Penny shares some girl talk with her friends about Leonard and his new girlfriend. ...
Sheldon and Amy decide to start several rumors about the others as a test. Meanwhile, Howard takes his relationship with Bernadette to even higher level.
When Leonard spends too much time in the shower with Priya, Sheldon charges Leonard with two violations of the roommate agreement. However, before he can get too far, Priya uses her skills as a ...
Raj attempts to cure his social anxiety disorder while Penny uses Bernadette to spy on Leonard and his girlfriend.
When Howard finally breaks the news to his mom that he's engaged to Bernadette, it lands her in the hospital.
When Bernadette receives her PhD, Wolowitz feels emasculated. Raj and Leonard swap places and Penny does something she's regrets.
In season five, Penny and Leonard's relationship is relaunched in full "beta test" mode, while Sheldon, Howard, and Raj discover the feminine mystique is something that cannot be ...
Penny is worried with how damaged her friendship with the guys will be in the aftermath of her sleeping with Raj while Sheldon becomes the leader of the paintball team.
A fight between Sheldon and Penny leaves Amy caught in the middle, while Leonard tries to spice up his long-distance relationship with Priya.
Leonard and Amy get to know each other better, while Howard and Bernadette spend the weekend with Mrs. Wolowitz.
Penny plays Matchmaker for Raj, which results in him finding a girl he is comfortable talking to.
Sheldon and Leonard get invited to a party at Wil Wheaton's house, and Howard gets an out-of-this-world opportunity.
Sheldon's mother, Mary Cooper, comes to visit, but Sheldon is annoyed that she also spends time with the rest of the gang, instead of catering to his every demand.
A cute comic book artist puts Leonard and Priya’s relationship to the test, while Sheldon tries to scare the guys for Halloween.
Amy becomes heartbroken when she discovers that Penny and Bernadette went wedding dress shopping without her.
Leonard and Penny try hanging out as friends on a 'non-date', but end up purposely ruining each others chances with perspective dates. Meanwhile, Sheldon enlists the help of Bernadette ...
When Stuart asks Amy out on a date, Sheldon must confront his feelings and consider where his relationship with Amy is going.