This chronology is a timeline of events that happened before the show began.
- May 7, 1974: Stuart is born
- February 26, 1980: Sheldon and Missy are born
- May 17, 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
- June 23, Between 1984 and 1987: Bernadette is born
- December 17, between 1979 and 1985: Amy Fowler is 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
- Sometime this decade: Stuart came to Pasadena and opened up the Comic Book Store.
- 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
- September 22, 2007: Leonard and Raj created an idea involving the conversion of footsteps into electromagnetic energy to make it possible for one to recharge their cell phone while walking.
- Before September 24, 2007: Penny breaks up with Kurt