Towards the end of the nineteenth century, with the advent of soil science, soils of the humid tropics were recognized as a separate entity called ‘tropical forest lateritic soils’. The term ‘lateritic’ was derived from laterite (Latin later, brick), a term coined by Buchanan (1807) to describe an iron-rich clay from south India which, when hardened upon exposure, was used as building material. Originally it was thought that laterite represented soil formations throughout the humid tropics, hence the generalization of the name to all red soils in the region. The great diversity of the tropical soils was realized only around the 1930s along with the limited areal occupation of laterite in the tropics. It was actually in Southeast Asia that Vageler (1930) and Mohr (1944) wrote the first two books on tropical soils, based essentially on their study of soils in Indonesia. The two volumes of Mohr’s book were published in Dutch in 1934–8. The English translation appeared in 1944. They attempted to classify soils of the tropics according to thickness, degree of weathering, parent material, and fertility. The understanding of the morphology, genesis, and distribution of soils in Southeast Asia evolved with the establishment and development of soil surveys in different countries of the region from the 1950s. A first overview was prepared by Dudal and Moormann (1964), using the 1938 and 1960 soil classification systems of the United States Department of Agriculture (USDA) (Baldwin, Kellogg, and Thorp 1938; Soil Survey Staff 1960). A revised version was in place by 1974 (Dudal, Moormann, and Riquier 1974). Preparation of a soil map of the world at a scale of 1:5 million started in 1961 at the initiative of the Food and Agricultural Organization of the United Nations (FAO), UNESCO, and the International Society of Soil Science (ISSS). In 1974 a unified soil classification was prepared and published (FAO 1974). A volume was specifically devoted to Southeast Asia (FAO 1979). The present chapter is based on this publication, and reference should be made to it and the accompanying map (1:5 million) for detailed information about the soils of the region.