This paper outlines a model of soil profile development in potential acid sulphate soils and their change into actual acid sulphate soils. Some such model is needed as a basis for soil survey and land evaluation, especially in tropical coastal wetlands where access is often difficult, local soil variations often confusing, and where vegetation and soil conditions change dramatically following any change in hydrology. Since this is a soil surveyor's model, emphasis is placed on identification of the situation in the field, even for these most chemical of soils.