Charge independence and symmetry are approximate symmetries of nature. The observations of the small symmetry breaking effects and the consequences of those effects are reviewed. The effects of the mass difference between up and down quarks and the off shell dependence q2 of p0 - w mixing are stressed. In particular, I argue that models which predict a strong q2 dependence of p0 -w mixing seem also to predict a strong q2 variation for the p0 - γ* matrix element, in contradiction with experiment.