24 Episodes · Premiered September 22, 2011 · Ended May 10, 2012
Penny regrets her sleeping with Raj and has become very good friends with Leonard, Leonard breaks up with Priya, Amy pushes Sheldon in their relationship eventually becoming boyfriend and girlfriend, Penny and the other women become a clique of their own, Howard prepares for his wedding and going into space to the International Space Station and Leonard asks Penny out as they begin "Leonard and Penny 2.0".
Penny worries that she's screwed things up permanently with her friends, while Sheldon takes command of the paintball team.
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.
Raj finally meets a girl he can communicate with.
Sheldon and Leonard get invited to a party at Wil Wheaton's house, and Howard gets an out-of-this-world opportunity.
Sheldon competes with the gang for his mother's attention when she comes to visit.
Cute comic book artist puts Leonard and Priya's relationship to the test, while Sheldon tries to scare the guys for Halloween.
Amy is crushed when Bernadette and Penny go shopping for wedding dresses without her.
Leonard and Penny try hanging out alone, and Sheldon must overcome his fear of birds.
Sheldon considers taking his relationship with Amy to the next level when Stuart from the comic book store asks her out on a date.
Leonard must face his fears after being contacted by his high school tormentor.
Sheldon gets in trouble with Amy when he isn't impressed by her recent accomplishment, and Howard must come to grips with Bernadette's dislike of children.
Everything might change when Leonard offers Penny a spur of the moment invitation to a romantic dinner for two.
Leonard and Penny experiment with dating, while Raj develops a peculiar relationship with his phone's virtual assistant.
Sheldon's selfish demands force Leonard to reconsider their friendship. Meanwhile, Wolowitz tries to pick his astronaut nickname.
When Sheldon is forced to take his vacation, he goes to work with Amy in her neurobiology lab. Meanwhile, Bernadette wants Howard to sign a pre-nup.
When an office at the University opens up, Sheldon must compete for it with his archenemy, Kripke. Meanwhile, a gift from Amy makes Penny uncomfortable.
Sheldon's life is turned upside-down after his barber gets sick. Meanwhile, astronaut training causes Wolowitz to rethink his decision to go into space.
Sheldon chooses to play video games with the guys rather than go with Amy to her aunt's birthday party.
Penny buys Leonard and Sheldon "Star Trek" collectibles as a thank-you, leading Sheldon to be haunted by Mr. Spock. Meanwhile, Raj decides he has met the "Future Mrs. Koothrappali" after his parents set him up on a date.
When Wolowitz gets to work with Stephen Hawking, Sheldon is willing to do anything to meet his hero.
Bernadette reconsiders marrying Howard after learning about his sexual history.
NASA reschedules Howard's mission, putting his and Bernadette's wedding plans in jeopardy. Meanwhile, Leonard says something surprising to Penny in the bedroom.
When Howard and Bernadette decide they want to be married before his NASA launch, the gang rushes to put on a wedding.
