The XXI International Materials Research Congress was held in Cancun, Mexico in August 2012. This Materials Research Society Proceedings contains papers presented at Symposium 2D "Structural and Chemical Characterization of Metals, Alloys and Compounds.” This special issue covers several aspects of the structural and chemical characterization of the materials in the following areas: metals, alloys, steels, composites, polymeric compounds, welding, nanomaterials, and surface coatings, among others. They are amorphous, crystalline, powders, coatings, 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), RAMAN spectroscopy, optical microscopy (OM), Fourier transform infrared spectroscopy (FTIR), differential thermal analysis (DTA), differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), thermo luminescence (TL), laser emission, etc. Theoretical models from these properties are included too.