Leonard inadvertently steals away the new woman Wolowitz thinks is the love of his life.
Leonard inadvertently steals away the new woman Wolowitz thinks is the love of his life.
Sheldon is thrilled when Leonard starts dating a woman who meets Sheldon's stringent standards.
Leonard asks Penny for advice when his new relationship starts moving too fast.
Penny starts dating Leonard's handsome colleague; Leonard and his friends are tortured by Sheldon's obsession with gift-giving etiquette.
Penny's criticism of Wolowitz's romantic life pushes him into depression and AWOL for a fighting robot battle the rest of guys are depending on him for.
Sheldon creates a scientific procedure for making friends.
Sheldon's solution to Penny's financial difficulty leads to a confrontation between Leonard and Penny's ex-boyfriend.
Leonard and Penny are drawn together after a disastrous visit from Leonard's mother.
A paintball game leads to a fight between Sheldon and Penny, and romance for Leslie and Wolowitz.
Leonard, Sheldon and Wolowitz are ecstatic to learn that a famous science-fiction actress (Summer Glau) is on board the train they are taking to San Francisco.
Penny's home business turns into a complete nightmare when Sheldon takes over.
Penny squares off with a new beautiful female neighbor who may become the building's "new Penny."
A fellow comic book enthusiast's hitting on Penny leads to Leonard and Howard going to a bar's Ladies' Night.
Leonard and Koothrappali escort a heartbroken Wolowitz to Las Vegas, and Sheldon becomes locked out of his apartment and must stay with Penny.
Penny's second date with Stuart sees her making a comment that gives Leonard new hope for a relationship with her. Wolowitz realizes there's a crucial error in a NASA project he's ...
The guys' plan to work over the summer at the North Pole makes Penny revaluate her feelings for Leonard.
When Sheldon learns the guys tampered with his expedition data he got from the arctic, he leaves to Texas in disgrace. This results in the guys following him, which threatens Leonard's hope ...
Leonard and Penny struggle to recover from an awkward first hookup while Sheldon and Howard stake their best comic books on a bet to determine the species of a cricket.
Howard and Raj visit a Goth nightclub to pick up women while Sheldon attempts to build a better Penny using chocolate-based behavior modification.
Raj must find a new job or be sent back to India, but Sheldon has a solution, which leaves Leonard and Penny dealing with Howard as a third wheel.
After overhearing that Wil Wheaton is entering a trading-card competition, Sheldon decides to enter it himself. Meanwhile, Penny sets up one of her friends on a date with Wolowitz.
Sheldon becomes Leonard's teacher in order to understand football, while an incident with flying a kite threatens Howard and Raj's friendship.
A squabble between Leonard and Penny sees Sheldon playing mediator, though out of his own incovenience from the sitiation rather than altruism.
With Leonard, Howard and Raj away camping in the desert, an injured Penny has only Sheldon to rely on.
After he's humiliated on National Public Radio, Sheldon vows to destroy Kripke, while Wolowitz tries not to destroy his new relationship with Bernadette.
Penny gets help from Sheldon in order to understand what Leonard's work is, while Wolowitz develops a jealousy when Leonard starts hanging out with his new girlfriend.
A Christmas visit from his mother has Leonard discovering she's kept a lot of news from him that she shares with Sheldon and worrying if she'll approve of his romance with Penny.
Leonard is aghast to find out a secret of Penny's: she believes in psychics. Meanwhile, Sheldon tries to assist Koothrappali in picking up a girl at a university mixer.
When their apartment is robbed, Leonard and Sheldon turn to their friends to create a state-of-the-art security system.
Sheldon's search for the answer to a physics problem leads him to work at the Cheesecake Factory with Penny.