The Decline of Western Civilization III is a 1998 documentary film, directed by Penelope Spheeris, that chronicles the gutter punk lifestyle of homeless teenagers. It is the third film of a trilogy by Spheeris depicting life in Los Angeles at various points in time. The first film, The Decline of Western Civilization (1981), dealt with the punk rock scene during 1980–1981. The second film, The Decline of Western Civilization Part II: The Metal Years (1988), covers the Los Angeles heavy metal movement of 1986–1988.

Spheeris later credited the 1998 film with having a profound effect on her. She began a relationship with a man she met while filming the movie, signed up to be a foster parent, and eventually fostered five children.