Acute respiratory infections (ARI) are a major cause of morbidity in children worldwide, and are estimated to cause four million deaths per year, mainly in the developing world. In those countries, bacterial infection with high case fatality is common, apparently following a primary viral infection. The case management strategy has had success in controlling severe outcomes. However, its dependence on the use of antibiotics and the advantage of primary prevention support the need for vaccines. Vaccines against viruses such as respiratory syncytial and parainfluenza would prevent what is often the initial infection and vaccines against Haemophilus influenzae and S. pneumoniae the major bacterial causes of mortality. Maternal immunization may have special relevance in developing countries where protection early in life is required. The development of combination vaccines would also be especially useful, since contacts with the medical system are often difficult. The introduction and use of new vaccines in those regions will require demonstration of cost effectiveness and acceptance by policy makers.