Physical properties, particularly index properties and water relations, are discussed using measurements on Caribbean soils, mostly from the islands of Nevis, Antigua and Dominica. Kaolin clays are shown to have a more active surface than montmorillonite when measured physical properties are expressed on the basis of surface area. The porosity of a clay soil is deter-mined by clay mineral type and proportion of larger soil grains. Content of clay-size grains is not a good index for predicting physical properties of tropical clay soils, and plasticity is evaluated as an alternative index. Plasticity depends upon the nature as well as the amount of surface, and is particularly useful for evaluating amount and activity of allophane. Water relation of clay soils are related to clay minerals and to swelling and cracking. The concept that 'management of clay soils is the manage-ment of cracks' is discussed. Measured values are presented for water retention, and water available to plants, for clay soils with different minerals.