Abstract The Cabibbo theory of semi-leptonic processes is examined on the basis of recent experimental and theoretical results. Although the gross features of the experimental situation conform with the theory, the detailed analysis is not completely satisfactory at the present time. Thus, the K e3 decay rates, the neutron lifetime, the Ξ − beta-decay rate, the asymmetry α Σ −e ( Σ − → n + e + ν), and the 26Al ft value require explanation or further precise experimentation. The problem of universality of weak interactions is discussed on the basis of two models which assume the validity of current algebra at small distances and for which the secondorder radiative corrections to G V/ G μ are finite: the first assumes a special form for the space-space part of the current algebra, the second assumes the existence of the intermediate boson. Although the present experimental situation as described by the 14O data is consistent with both models, it is possible that a clarification of the K e3 decay rates and the “ 26Al problem”, as well as precise calculations of symmetry-breaking corrections to K e3 amplitudes, may discriminate against one of them. The need for accurate calculations of second-order symmetry-breaking effects to vector matrix elements and of electromagnetic corrections of order Zα 2 is emphasized.