What can low-energy nuclear physics tell us about elementary particles and quarks?

A pedagogic review is presented, for the benefit of the non-particle physicist, of recent remarkable conclusions drawn from the ft values of various superallowed nuclear decays, which are known to great accuracy - such accuracy, in fact, that radiative corrections have to be taken into account to compare the theory with experiment. The calculation of these radiative corrections has recently become possible using the Weinberg-Salam unified gauge theory of weak and electromagnetic interactions as applied to the quark model of elementary particles, and making use of Cabibbo universality, which relates the coupling constants for nuclear decay and muon decay. The good agreement between theory and experiment provides a confirmation of these theoretical models. It is, however, not possible to say whether quarks have integral or fractional charge.