The fourth season of the television series Buffy the Vampire Slayer premiered on October 5, 1999, on The WB and concluded its 22-episode season on May 23, 2000. It maintained its previous timeslot, airing Tuesdays at 8:00 pm ET. Beginning with this season, the character of Angel was given his own series, which aired on The WB following Buffy. Various Buffy characters made appearances in Angel, including Buffy herself; Cordelia Chase, formerly a regular in Buffy, and Wesley Wyndam-Pryce, who appeared in Buffy season three.

Buffy the Vampire Slayer is an American supernatural drama television series created by writer and director Joss Whedon. The concept is based on the 1992 film, also written by Whedon, although they are separate and unrelated productions. Whedon served as executive producer and showrunner of the series under his production tag Mutant Enemy Productions. It premiered on March 10, 1997, on The WB and concluded on May 20, 2003, on UPN.