There is a need for materials of exceptional hardness in order to coat mechanical components. One way to do this is take advantage of the properties of nanostructured materials. This book gives an insight into a broad range of fields related to hard coatings, from their deposition and characterization up to the hardening and deformation mechanisms allowing the interpretation of results. In addition to the above-mentioned hardness, this type of coating often needs mechanical properties such as excellent adhesion to the substrate and very high fracture toughness and other requirements. Their use in chemical aggressive environments at very high temperatures demand also very high oxidation/corrosion resistance and thermal stability. Thus, increasing worry has being adopted by researchers in this field concerning the development of coatings that could present simultaneously all the necessary properties to guarantee a successful implementation in real mechanical applications.