Soil shrinkage caused by the removal of water by trees and other vegetation can result in foundation subsidence. Soil swelling caused by the recovery of moisture following tree removal can result in foundation heave. This Digest gives simple guidance on minimising these effects in clay soils and points to some dangers in current foundation practice. Table 1, based on data collected by the Royal Botanic Gardens Kew, ranks tree species according to the risk of damage from them. This paper also discusses methods of protecting trench fill foundations from swelling pressures.