Leonard and Penny renew their vows, this time inviting their friends and family for wedding party; they also learn that marriage is about compromise, and figure out how to support each other. Sheldon and Amy experiment to take their relationship to the next level, and after an emotional struggle they move in together in Penny's old apartment. Howard and Bernadette realise that being a parent is a full-time job, but with the help of their friends they manage to find joy in raising their child. When his friends tell him he's extremely spoiled, Raj decides to stop taking his father's money and learn how to make ends meet.

This season, Leonard gets a girl. So does Sheldon. Howard drives the Mars Rover into a ditch. Raj woos a terminator. Gorgeous girl-next-door Penny falls under the spell of Age of Conan. And super-smart, ueberconfident Leslie Winkler reduces mere men to spineless jellyfish.

University physicists Leonard and Sheldon know whether to use an integral or a differential to solve the area under a curve. But they don't have a clue about girls. Or dating. Or clothes. Or parties. Or having fun. Or, basically, life. So when a pretty blonde named Penny moves in the apartment across the hall, the guys decide to get an education outside of the classroom. Boys, you have a lot to learn.