This article provides an overview of recommendations for HIV surveillance. Results of surveillance are used in practice to inform program decisions, judge the effectiveness of the national response, lobby for effective programs, and to provide accurate measures of trends and the absolute state of the epidemic. Recommended surveillance activities differ for different epidemic situations-epidemics that are concentrated in defined groups with high-risk behavior, and epidemics that are well established among heterosexuals in the population at large. Surveillance systems in countries with different levels of the epidemic face major challenges, most of which revolve around identifying and obtaining information from representative samples of the at-risk populations. A brief examination of surveillance systems in Botswana and Vietnam illustrate how these challenges are being met in practice. While there is room for improvement, HIV surveillance systems in many developing countries are relatively robust, and are growing stronger all the time. In most countries, however, insufficient use is made of the information generated by these systems in terms of strengthening HIV prevention and care programs.