This paper reviews research on improvement and fertilization of acid sulfate soils in Thailand carried out by two major institutions of the Ministry of Agriculture and Cooperatives (MAC), the Department of Agriculture (DA) and the Land Development Department (LDD) and only one of the institutions in the Government University Bureau (GUB), Kasetsart University (KU). Subjects investigated separately by the three organizations are reviewed and discussed under three categories of land suitability classes for paddy P II a, P III a and P IV a, recognized by Thai soil scientists. The results of the cooperative project on "Rice Yield Improvement in Acid Sulfate Soils" by the working committee organized within the MAC is presented and discussed separately.