The Big Bang Theory

CBS | 8:00 pm

This blockbuster sitcom closes out its 12-season run with a one-hour finale. CBS is holding back details, but longtime pals Leonard Hofstadter and Sheldon Cooper (Johnny Galecki, Jim Parsons) — who have spent most of their adult lives living either together or within a few yards of each other — may be heading in different directions with their lives. Kaley Cuoco, Simon Helberg, Kunal Nayyar, Melissa Rauch and Mayim Bialik also star. A half-hour retrospective special also airs later this evening.