A review is presented of the present status of research on the influence of magnetic fields on photoprocesses in organic solids. This influence manifests itself in a change of the photoconductivity or luminesence of molecular crystals in weak magnetic fields at room temperatures Q/H$\ll$kT). The magnetic effects on photoconductivity, luminescence, and photooxidation are considered together with a theoretical interpretation of these effects, based on allowance for the change of the eigenfunctions of the interacting paramagnetic particles in the Zeeman effect.