AIDS is an epidemic and has its effect all over the world. Unfortunately, worst effected are the developing countries which rely on international donors for the implementation of HIV intervention programmes. There is a growing need to develop cost effective methods and their proper implementation especially in high risk groups like commercial sex workers. HIV prevention interventions in developing countries can reduce the incidence of HIV infection and sometimes save financial resources in the process. Cost-effectiveness analysis (CEA) is a type of economic analysis where both the cost and the outcome (impact, result, effect, benefit, health gain ...) of an intervention are evaluated. This book is a literature review of modeling the impact and cost-effectiveness of HIV prevention programmes in Commercial sex workers in developing countries.