According to the World Health Organization, infectious diseases account for more than 13 million deaths every year, including nearly two-thirds of all deaths among children under age 5. Infectious diseases present a substantial threat to people in all parts of the world, and this threat has grown in volume and complexity. New diseases have emerged, others once viewed as declining in significance have resurged in importance, and many have developed substantial resistance to known antimicrobial drugs. Infectious disease surveillance provides national and international public health authorities with information that they need to plan and manage efforts to control these diseases. In the mid-1990s, public health experts in the United States and abroad determined that global infectious disease surveillance was inadequate, and both the World Health Assembly and the President of the United States called for the development of an effective global infectious disease surveillance and response system. The strongest influence on the evolution of the current global infectious disease surveillance framework has been the international community's focus on specific diseases or groups of diseases. The international community has created diverse surveillance programs to support global and regional efforts to control particular diseases. Surveillance systems in all countries suffer from a number of common constraints. However, these constraints have their greatest impact in the poorest countries, where per capita expenditure on all aspects of health care amounts to only about three percent of expenditures in high-income countries. Surveillance in developing countries is often impaired by shortages of human and material resources. The international community recently launched several initiatives that may improve global surveillance. The community has committed itself to reducing the global burdens imposed by three diseases--tuberculosis, human immunodeficiency virus/acquired immunodeficiency syndrome, and malaria. The community has also begun more broadly targeted initiatives to upgrade laboratories, strengthen epidemiological capacity, and otherwise improve surveillance for infectious diseases as a whole.