The Big Bang Theory - All Seasons

The lives of physicists Dr. Leonard Hofstadter and Dr. Sheldon Cooper are shaken up when an attractive young aspiring actress from Omaha, Nebraska named Penny moves into the apartment across the hall from theirs. Leonard begins to become hopelessly enamored of Penny, while she feels only platonic affection for him; as a result, she finds herself putting up with his closest and ever-present friends: his roommate, Sheldon, who appears borderline obsessive-compulsive; engineering whiz Howard Wolowitz, a desperately sex-crazed mama's boy who thinks that his 1960s-style clothing and hairstyle give him an air of cool hipness; and Dr. Rajesh "Raj" Koothrappali, who will not speak to her as he is too shy to talk to women (a case of selective mutism), unless intoxicated in which case he becomes a smooth talking yet highly overly aggressive womanizing flirt.

Leonard and Penny's relationship takes a turn for the worse when they break up, but is quickly resolved. Soon their relationship progresses into a stronger friendship than before, while Sheldon and Penny's friendship slowly begins.

Penny throws herself at Leonard after he returns from three months at the North Pole and they begin a relationship, Penny and Sheldon start a quirky friendship though she can still annoy him, Howard begins to date Bernadette Rostenkowski and Sheldon meets Amy Farrah Fowler.

Sheldon begins a platonic relationship with Amy, Howard reconnects with Bernadette eventually asking her to marry him, Leonard begins to date Raj's sister Priya, Penny becomes friends with Amy and expresses regret at breaking up with Leonard.

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".

Howard return from space and adjust to normal, married life on earth. Sheldon and Amy's unique relationship continues to progress, though at a slower pace than Amy wants. Leonard and Penny's relationship is business as usual, with Leonard once again proposing to Penny. Meanwhile, Raj finally meets a girl and enters a (somewhat) stable relationship, the demise of which leads to unexpected progress for Raj.

Sheldon and Amy's relationship takes a step forward, Penny makes big decisions in her professional and person life, Raj tries to prosper in the dating world with his newfound ability to talk to women, and Howard treats Bernadette to a very special surprise for the anniversary of their first date.