The effect of both electron and proton irradiation of silicon photovoltaic cells is given in terms of the lossof photovoltaic response and the decrease in the lifetime. Analysis of the spectral response shows that asimple carrier diffusion model provides an adequate description of the behavior of the shallow-diffusedjunctions that were investigated, and yields values for the minority carrier diffusion length before and afterirradiation. Most of the photovoltaic response is shown to occur in the base region of the cells, rather thanin the surface layer, and virtually all of the loss of response is caused by defects introduced in the base. Thereciprocal of the lifetime is linear with the cumulative irradiation flux, and is consistent with the loss ofphotovoltaic response. There are significant differences betweenponnandnonpcells under electronbombardment; the former damaging roughly 100 times as rapidly as the latter. Under proton bombardmentthe difference is roughly a factor of three. A comparison of electron, proton, and neutron irradiation suggeststhat the individual lattice displacements produced in electron irradiation are no more effective in producingrecombination than the displacements produced in high concentration in neutron and proton irradiation.