Cher Horowitz lives in a Beverly Hills mansion with her father Mel, a $500-an-hour litigator; her mother died from an accident during a routine liposuction procedure when Cher was a baby. Cher is attractive, popular, and wealthy. She attends Bronson Alcott High School. Cher's best friend is Dionne Davenport, who is also wealthy and beautiful. Dionne has a long-term relationship with popular student Murray; Cher claims that this is a pointless endeavor for Dionne.
Josh, Cher's socially conscious ex-stepbrother, visits her during a break from college. Josh and Cher spar continually but playfully. She mocks his idealism, while he teases her for being selfish, vain, and superficial, and says that her only direction in life is "toward the mall". Cher plays matchmaker for two hard-grading teachers at her school, Mr. Hall and Miss Geist. She facilitates the relationship between the teachers in order to make them relax their grading standards so she can renegotiate a bad grade on her report card. But after she sees their newfound happiness, she realizes she enjoys doing good deeds. Cher then decides to give back to the community by "adopting" a "tragically unhip" new girl at school, Tai Frasier. Cher and Dionne give Tai a makeover, which gives Tai confidence and a sense of style. Cher also tries to extinguish the attraction between Tai and Travis Birkenstock, an amiable skateboarding slacker, and to steer her towards Elton, a popular and wealthy student.
Elton rejects Tai and unsuccessfully attempts to seduce Cher. A handsome new student at their school named Christian becomes Cher's target boyfriend. Murray explains to Cher and Dionne that Christian is gay. Despite the failure of this endeavor, Cher remains on friendly terms with Christian, primarily due to her admiration of his taste in art and fashion. Matters take a turn for the worse when Tai's newfound popularity strains her relationship with Cher. Cher's frustration escalates when she fails her driving test and cannot change the result. When Cher returns home, crushed, Tai confesses her fancy for Josh. Tai wants Cher's help in pursuing Josh. Cher says Tai is not right for Josh and they quarrel. Cher and Tai's disagreement ends with Tai calling Cher a "virgin who can't drive". Feeling "totally clueless", Cher reflects on her priorities and her repeated failures to understand or appreciate the people in her life.
After thinking about why she is bothered by Tai's interest in Josh, Cher realizes that she loves Josh. She begins making awkward but sincere efforts to live a more purposeful life, including captaining the school's Pismo Beach disaster relief effort. Cher and Josh eventually admit their feelings for one another, culminating in a tender kiss. Ultimately, Mr. Hall and Miss Geist wed; Cher's friendships with Tai and Dionne are solidified; Tai and Travis are in love; and Cher catches the wedding bouquet, helping Josh win a $200 bet. She embraces Josh and they kiss.