6 Series, 140 Episodes
Leonard and Sheldon are brilliant physicists, but have no luck when it comes to understanding women. All this begins to change when the beautiful Penny moves in next door.
Sheldon is bothered by how messy Penny's flat is and he sneaks in to clean and organise it, but Penny isn't best pleased when she finds out
Leonard is depressed when he discovers that Penny is seeing someone, and he actually summons up the courage to ask a woman out on a date
Getting fired forces Sheldon to ponder life outside physics, leaving Leonard to take drastic action to snap his friend out of his reverie
Leonard worries that he's wasting his time on Penny, so he gets closer to Leslie. Meanwhile, Sheldon frets over a change to his hamburger routine.
Penny hosts a Halloween party, putting Leonard, Sheldon, Howard and Raj through a new test of their social skills. Perhaps unsurprisingly, they fail it miserably...
When Howard seduces Penny's friend and spends the night with her in Penny's flat, Penny asks if she can sleep on Leonard and Sheldon's sofa
Raj panics when his parents arrange a blind date for him, but discovers that he actually can talk to women after a few drinks
Sheldon and Leonard are asked to present a paper at a physics conference, but Sheldon is reluctant to share the credit. Penny tries to help.
Leonard and Sheldon each tell a lie to avoid going to see Penny on stage singing in a production of Rent, but Sheldon's lie gets out of control
Penny volunteers to nurse Sheldon when he's sick. However, his friends know how miserable he is when he's ill and stay well away from him.
When Sheldon meets a 15-year-old physicist who is clearly much brighter than he is, his confidence is shaken to the core
Sheldon is ousted from the gang's Physics Bowl quiz team, so he decides to prove his superiority by forming his own team for the event
Penny makes fun of Leonard's habit of collecting goofy memorabilia, but his friends kick up a fuss and try to keep him on the side of the nerds
Sheldon's twin sister Missy is in town and, bizarrely, she's a stunner! Leonard, Howard and Raj compete for her attention, but then Sheldon declares he will decide who dates his sister...
Penny wants to throw a surprise party for Leonard and gets support from Howard and Raj, but Sheldon's indulgence in an electronics shop throws her off track
When Penny breaks up with her boyfriend, Leonard plucks up the courage to ask her out. Both of them then ask Sheldon for advice about the date.