The specific aim of the proposed project is to enhance our understanding of how to sustain recent improvements in contraceptive use at first sex so that teens and young adults can become more consistent contraceptive users. The proposed project will examine patterns of contraceptive use and consistency across sexual relationships, within current cohorts of teens and young adults. Our premise is that contraceptive use must be negotiated and sustained within each new sexual relationship. Understanding why teens and young adults use contraception consistently, as well as understanding patterns of inconsistent use, will help inform strategies to prevent unintended pregnancy and STIs. Analyses by race/ethnicity will help address disparities in reproductive health among racial and ethnic minorities. Additional sub-population analyses will include comparisons of teens and young adults, and males and females. The proposed project will incorporate an ecological framework, which posits that behaviors among teens and young adults will be influenced by factors from multiple domains of their lives. We will incorporate multi-level and multi-process models to examine how contraceptive use patterns are shaped by individual knowledge and motivations, characteristics of each sexual relationship (including partner characteristics and sexual activity), peer environments and family background, including parent-child communication. We will also examine the influence of school, community, and policy variables, such as sex education programs and the presence of economic opportunities. The project will analyze month-by-month histories of contraceptive use and sexual relationships within two cycles of the National Survey of Family Growth (1995, 2001) and information on sexual relationships and contraceptive use patterns within three waves of the National Longitudinal Study of Adolescent Health.