When casual viewers ask, “How many Big Bang Theory series are there?”, the most straightforward answer is one —the original CBS sitcom that aired for 12 seasons from 2007 to 2019. However, for fans and scholars of modern television, the question is more nuanced. The Big Bang Theory (often abbreviated as TBBT) has expanded into a genuine media franchise, including a successful prequel series, a spin-off in development, and various digital shorts. Therefore, a truly useful answer distinguishes between the original show and its extended universe. The Original Series: The Core of the Franchise The flagship series, The Big Bang Theory , created by Chuck Lorre and Bill Prady, follows a group of socially inept but brilliant scientists—Leonard Hofstadter, Sheldon Cooper, Howard Wolowitz, and Raj Koothrappali—and their aspiring actress neighbor, Penny. Over 12 seasons and 279 episodes, the show evolved from a niche comedy about nerd culture into a mainstream ratings juggernaut. This single series remains the definitive answer for most viewers. It concluded on May 16, 2019, with a two-part finale that earned over 18 million viewers, solidifying its place in television history. The Prequel Series: Young Sheldon The most significant expansion of the franchise is Young Sheldon , which premiered in 2017, midway through TBBT’s original run. This prequel series shifts from a multi-camera laugh-track format to a single-camera family comedy-drama. It chronicles the childhood of Sheldon Cooper growing up in East Texas, exploring his prodigious intellect and social struggles within his working-class family.