Educators, service providers, and health professionals worldwide are advocating that young people receive comprehensive sexuality education to help them become sexually healthy adults and to help them practice safer sexual behaviors, delay the onset of sexual intercourse, and reduce unplanned pregnancy and sexually transmitted disease (STD) rates. Though there is often consensus that young people should receive such education, few actually do. This is primarily due to a lack of understanding and consensus about sexuality education goals, components, and standards. Educators, providers, and policymakers frequently ask: “What are the goals and objectives of such education?” “What are the topics?” “What are the developmental messages?” “When and how should young people receive these messages?” This handbook, Developing Guidelines for Comprehensive Sexuality Education, will answer those questions as it shares SIECUS’s experiences in developing guidelines in the U.S. and internationally.