The empirical evidence for vertical piles under horizontal or lateral loading is firstly reviewed. The load–deflection relationship is nonlinear from the early stages of loading, while the load–moment relationship is nearly linear. Moving from the available experimental evidence, typical design issues are addressed and a validation of the widespread Broms’ method is then carried out. To predict the pile–soil interaction, a computer code, NAPHOL, based on a hybrid BEM approach, is fully presented and discussed. A limiting pressure profile, coupled with a cut-off procedure, allows the method to cope with the nonlinear behaviour. Simple guidelines and equations, to calibrate the model parameters, are derived on the basis of the back-analysis of a significant number of case histories. The program is finally used to throw light on the mechanism of the pile–soil interaction under horizontal loading.