The largest generation of adolescents in history - 1.2 billion strong - is preparing to enter adulthood in a rapidly changing world. This UNFPA publication examines the challenges and risks they face. It finds that investing in young people will yield generous returns, but that their needs continue to be shortchanged. An estimated 238 million youth - almost one in four - face the constraints of extreme poverty. Providing age-appropriate information about sexualityand promoting responsible and safe behaviour, including abstinence, is essential to reducing adolescentpregnancy and stemming the HIV/AIDS epidemic. With the age of marriage increasing and sexual activity often occurring earlier, far greater access to youth-friendly sexual and reproductive health services is needed to reduce widespread adolescent pregnancy and high rates of sexually transmitted infections and HIV/AIDS.