After a brief review of a number of developments of unsaturated soil mechanics, the paper presents some applications to engineering problems. The first case involves the collapse of a residual soil in Brazil triggered by a water level increase caused by the filling of a dam reservoir. The second case analyzes the effects of rainfall on a natural slope in Ancona (Italy). The final case refers to the subsidence in the region of Ravenna related to the depletion of deep gas reservoirs. The ensemble of the cases described illustrates the potential of unsaturated soil mechanics concepts for the understanding and reproduction of observed field behaviour.