This Materials Research Society Proceedings contains papers presented at Symposium 3 "Structural and Chemical Characterization of Metals, Alloys and Compounds" of the XX International Materials Research Congress. This event is intended as a forum for the dissemination of research results on materials science. The volume covers several aspects of the structural and chemical characterization of the materials in the following areas: metals, alloys, ceramics, steels, composites, polymeric compounds, welding, nanomaterials, and surface coatings, among others. They are amorphous, crystalline, powders, fibers, thin films, etc., which were prepared with different techniques. The structural characterization techniques included scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), optical microscopy (OM), mechanical characterization, atomic absorption, luminescence, thermo luminescence, energy transfer, photorefractive effect, birefringence, photo catalysis, photoconductivity, birefringence, laser emission, etc. Theoretical models from these properties are included, too.