Werner Kirsch, Peter Stollmann, G\"unter Stolz Localization for random perturbations of periodic Schr\"odinger operators (96K, LaTeX) ABSTRACT. (This is a revised version of a preprint posted in 9/96.) We prove localization for Anderson--type random perturbations of periodic Schr\"odinger operators on ${\bf R}^d$ near the band edges. General, possibly unbounded, single site potentials of fixed sign and compact support are allowed in the random perturbation. The proof is based on the following methods: (i) A study of the band shift of periodic Schr\"odinger operators under linearly coupled periodic perturbations. (ii) A proof of the Wegner estimate using properties of the spatial distribution of eigenfunctions of finite box hamiltonians. (iii) An improved multiscale method together with a result of de Branges on the existence of limiting values for resolvents in the upper half plane, allowing for rather weak disorder assumptions on the random potential. (iv) Results from the theory of generalized eigenfunctions and spectral averaging. The paper aims at high accessibility in providing details for all the main steps in the proof.