Reliable evidence on the results of investments at the community level is in short supply. While communities have played a large role in the HIV/AIDS response, their contributions and innovative approaches to HIV prevention, treatment, care and support have not always been the focus of systematic and rigorous evaluations. To address this gap, seventeen analytical pieces were undertaken including evaluations in Burkina Faso, India, Kenya, Lesotho, Nigeria, Senegal, South Africa and Zimbabwe over a three -year period (early 2009 to early 2012) to build a robust pool of evidence on the effects of community based activities and programs. Due to the complexity and varied nature of community responses, the evaluation attempted to determine the results that investments have produced at the community level by applying a mixed method approach: Randomized Control Trials (RCT), quasi-experimental studies, qualitative studies, and analytical studies including financial data. Specifically, the studies examined a typology of community response and the flow of funds to community based organizations, while investigating the impact of the community responses on (i) knowledge and behavior, (ii) use of services, (iii) social transformation, and (iv) HIV incidence. Evaluation findings indicate that investments in communities have produced significant results at the community level, which contribute to outcomes at the national level, all while leveraging limited resources. A unique feature of this multi-country evaluation is the collaboration between the World Bank and the UK DFID and of these agencies with a major civil society network: The UK Consortium on AIDS and International Development. Another key feature is the sustained consultation process with civil society and stakeholders at the local, national and global levels. The book's findings are promising: At varying levels, ranging from causal to suggestive evidence, depending on the country context, the HIV response in communities can improve knowledge and behavior, and increase the use of health services, and even decrease HIV incidence. Evidence on social transformation was more mixed, with community groups found to be effective only in some settings. Each study in the evaluation provides a partial view of how communities shape the local response; however, taken together they constitute a significant pool of rigorous evidence on the contributions of communities, community groups and civil society to the national and global HIV/AIDS response.