The paper sets out a framework for investigating the possible causes of foundation failures in a systematic manner. Aspects relating to foundation failure such as conditions for failure, factors affecting geotechnical foundation resistance, structural foundation resistance, factors affecting applied loads and structural actions, development and testing of credible hypotheses are discussed. Attention is confined to foundation failures (ultimate failure conditions), although similar principles can be applied to cases involving excessive deformations of the foundation system (serviceability failures). An example is then presented to illustrate the application of the approach developed to a case involving failure of a piled foundation.