This book is an attempt to capture a rich and growing experience with a remarkable strategy to prevent the transmission of HIV where it is associated with heterosexual transmission linked to sex work: the 100% condom use program. First pioneered in Thailand, followed by Cambodia, this strategy has been expanded to Vietnam, China, Myanmar, Mongolia, the Philippines, and the Lao People's Democratic Republic. This publication attempts to review the experience from all these countries and to elucidate the lessons learnt and challenges that remain.