Using data from the Relationship Dynamics and Social Life Study, a diverse sample of 925 women updated weekly for 2.5 years, I (1) describe how desire for sex varies across and within women during the transition to adulthood; (2) explore how desire corresponds with women’s social circumstances and experiences; and (3) assess the relationship between desire for sex, sexual activity, and contraceptive use. The strength of young women’s desire varies across demographic characteristics like religiosity and social class; changes after pivotal events like sexual debut; and varies with social ecology, such as friends’ attitudes. When women more strongly desire sex they are more likely to have sex and to use hormonal contraception. Moreover, the association between desire and sex is especially pronounced when women are using a hormonal method. In contrast, when women more strongly desire sex they are less likely to use condoms or withdrawal, irrespective of hormonal use. These findings suggest that sexual desire is socially situated and relevant for both anticipatory and situational decisions about contraception.