The control of disease caused by infectious agents or their toxic products. Successes in the 19th and 20th centuries in the treatment and control of communicable diseases such as smallpox, cholera, tuberculosis, gastrointestinal infections, poliomyelitis and sexually transmitted diseases resulted in an erroneous conception that they no longer posed a serious threat to public health, and certainly not in developed countries. As a consequence, the maintenance of effective public health strategies steadily lost out in the competition for resources to the more ‘glamorous’ developments in medicine, such as improved cancer treatments, heart surgery, kidney dialysis and organ transplantation. However, in recent decades the dangers of this approach have become increasingly apparent. Rapidly expanding urban populations, more complex lifestyles, new and resurgent infections (some linked to a spread of antibiotic resistance) such as AIDS/ HIV and variant creutzfeldt-jakob disease, and the ease with which infection can be spread by the enormous growth of long distance travel and population migrations are severely straining existing public health measures. The supply of clean water, effective waste- and sewage-disposal measures, the hygienic production and delivery of food and early detection and subsequent prevention of, infectious diseases can no longer be taken for granted. Governments will need to strengthen the provision of workable, properly resourced public health facilities, and developing countries will need financial support and expert help from developed nations to achieve this objective. Timely recognition of new and resurgent infectious diseases requires national and international early-warning mechanisms to ensure rapid investigation and implementation of effective control measures. Otherwise, serious breakdowns in public health will occur, and international co-operation is vital to provide and support control measures.