This chronology is a timeline of events that happened before the show began.
- Sometime between 1974 - 1980 in May: Stuart is born
- February 26, 1980: Sheldon is born
- May 1980: Leonard is born
- March-September 1981: Howard is born
- October 6, 1981: Raj is born
- 1985: Sheldon's grandfather, Pop-Pop, dies
- December 2, 1985: Penny is born
- Between 1980 and 1989: Bernadette and Amy are born
- 1986-1987: Leonard, six years old at the time, walks in on his naked parents and his mother is swatting his father with Leonard's new ping-pong paddle
- 1991: Sheldon starts college at age 11
- 1994: Sheldon graduates from college at age 14
- 1994: Sheldon's father dies
- 1995: Sheldon attends Comic-Con to meet Wil Wheaton; when Wil doesn't show up, this fuels Sheldon's longtime hatred for him.
- 1996: Sheldon receives his doctorate.
- 1997-1998: Penny rebuilds a tractor engine all by herself at age 12
- 2000: Amy begins training in the field of neurobiology
- 2003: Sheldon and Leonard meet for the first time; the duo also meet Howard and Raj
- 2003: The Elevator to the Apartment Building is destroyed
- 2004: Leonard earns his doctorate and officially becomes a doctor.
- 2003-2007: Penny moves to Pasadena, starts dating Kurt, and gets a job at The Cheesecake Factory