Promotion of the low risk “ABC” behaviors—Abstinence, Being faithful, and Condom use—has had only limited success in Africa. This book draws on a large qualitative study affiliated with an adolescent intervention trial to examine how ABC promotion can be improved. It evaluates the MEMA kwa Vijana sexual health program, which was implemented in 62 primary schools and 18 health facilities in rural Tanzania, scrutinizing its teacher-led curriculum, peer education, youth-friendly health services, youth condom distribution, and community mobilization components. The book examines how implementing such a low-cost, large-scale program involved many compromises, including those between national policies and international “best practice” recommendations, between the most desirable intervention design and one that was affordable and sustainable at a large scale, between optimal teaching methods and real-world teaching capacity, between ideal curriculum content and what was acceptable to the local community, and between adults’ values and youths’ realities. The program’s impact is evaluated by triangulating findings from three person-years of participant observation, in-depth interviews, survey interviews, and biomedical tests. The book also provides in-depth case studies to examine the motivations and strategies of extraordinary young people who practiced ABC behaviors. It outlines broad principles for ABC promotion, including: acknowledging existing youth sexual relationships; promoting each low risk behavior in complexity and depth; working with preexisting, culturally compelling motivations; and intervening at individual, interpersonal, community, and structural levels. Many recommendations for the promotion of specific ABC behaviors are discussed, such as reducing pressures and incentives for girls to have sex; targeting male risk-perception and self-preservation; promoting alternative forms of masculinity than sexual conquest; strengthening premarital and marital relationships; tailoring fidelity programs for hidden couples, couples planning to marry, and monogamous and polygynous married partners; and addressing pleasure, trust, pregnancy prevention, and fertility protection in condom promotion. The book concludes with additional recommendations specific to school programs, and a review of promising complementary interventions for out-of-school youth, women, men, couples, and parents.