The focus of this issue is on global advances in conducting monitoring and evaluation (M&E) of the global response to the HIV/AIDS epidemic. Only by implementing comprehensive and sustainable M&E systems will we know how much progress we are making, as nations and as a global community, in combating this pandemic. The chapters primarily focus on developing nations and are presented largely from the perspective of evaluators working for donors, international agencies, and national governments. Although it is clear that a comprehensive M&E system must eventually include both monitoring and evaluation, the initial aim has been to establish a foundation derived largely from surveys and monitoring information. To date, much of the focus in M&E has come from the global level because new global funding initiatives been launched and required rapid scale-up and the development of technical guidance, international standards, and indicators for monitoring progress and determining success. At the regional and country levels, the challenge has been to implement national M&E plans and systems within a context of overall low M&E capacity and a range of M&E needs.