[en] In an attempt to examine the possible compositeness of quarks and leptons, experiments relevant to the non-point-like nature of these fermions were reviewed. Data were used to deduce limits on the substructure energy scale. Some specific models of quark and lepton structure proposed recently were discussed. Emphasis was focused on which predictions could be tested experimentally. Experiments were developed which could increase the energy range in which substructure could be probed and thus provide a more realistic basis on which to discuss compositeness