The film tells the story of Cher Horowitz (Alicia Silverstone), a good-natured but superficial girl. Cher is attractive, popular, and extremely wealthy. At a few months shy of sixteen, she has risen to the top of the high school social scene and is happy and self-assured in her insular, fashion-obsessed world. She lives in a Beverly Hills mansion with her father (Dan Hedaya), a ferocious $500-an-hour litigator; her mother has long since died, having succumbed to complications while undergoing liposuction. Cher's best friend is Dionne Davenport (Stacey Dash), who is also rich, pretty, and hip, and understands what it's like to be envied.
Among the few people to find much fault with Cher is Josh Lucas (Paul Rudd), her socially conscious ex-stepbrother who visits during a break from college. Josh and Cher spar continually but without malice; she refers to him as "granola breath" and mocks his scruffy idealism, while he teases her for being selfish, vain, and superficial, and says that her only direction in life is "toward the mall."
Illustrating that Cher's selfishness is usually innocent and relatively harmless, Cher plays matchmaker for two lonely, nerdy, hard-grading teachers, Mr. Hall (Wallace Shawn) and Miss Geist (Twink Caplan). She achieves her original purpose to make them relax their grading standards so she can renegotiate a bad report card but when she sees their newfound happiness, she realizes she likes doing good deeds. Cher now decides that the ultimate way she can give back to the community would be to "adopt" a "tragically unhip" new girl at school, Tai Frasier (Brittany Murphy). Cher and Dionne give Tai a makeover and initiate her into the mysteries of popularity. Cher also tries to extinguish the strong mutual attraction between Tai and Travis (Breckin Meyer), an amiable skateboarding slacker, and to steer her toward Elton (Jeremy Sisto), a rich snob.