Over one thousand million people live in the tropical regions of the world, most of them in developing countries where living standards are lower than in the countries of the temperate climatic zones. Fanger has suggested, although historical, cultural and political reasons may be found to explain this difference, it seems likely that the severe heat stress, to which people living in the tropics are exposed for most of their lives, has contributed to the lower degree of economic and industrial development found there. Within the next century it is probable that a large proportion of the population of the tropics will live, work, and play in air-conditioned buildings. At present, air conditioning is generally confined to essential industrial and military applications, or to prestige government, commercial, and residential developments. Tropical climates may be broadly categorized as either "hot and dry", or "warm and wet". This paper considers the application of air conditioning in three areas in the northern latitudes between the Tropic of Cancer and the Equator.