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 characterisation 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, fibres, thin films, etc. which were prepared with different techniques. The structural characterisation techniques included scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), optical microscopy (OM), mechanical characterisation, atomic absorption, luminescence, thermoluminescence, energy transfer, photorefractive effect, birefringence, photo catalysis, photoconductivity, birefringence, laser emission and so on. Theoretical models from these properties are included as well.