The structure of two-component coatings codeposited by magnetron sputter ion plating was studied. This apparently simple topic has never been studied systematically and has led to a number of unexpected and very interesting results. The systems that were studied included materials with 100% solid-solubility, (titanium and zirconium) totally insoluble materials (chromium and copper) and materials that can form intermetallic compounds (titanium and aluminium). Variables studied included method of deposition, composition of the coating and energy of ion bombardment during deposition. Two approaches were used for the deposition process. These were multilayer deposition from vertically opposed magnetrons and codeposition from coplanar magnetrons, both using closed field magnetic arrays. Both methods are fundamentally the same. It is the orientation and manipulation of the substrates during the deposition process which leads to either a multilayer coating structure or a codeposited homogeneous coating. The flexibility of the coating technique was demonstrated and a greater understanding was gained of both the structure and properties of alloy coatings and how these are influenced by the deposition parameters in a magnetron sputtering system. The coating structures were studied using SEM and XRD and their properties by different mechanical tests. Prior studies in this field have shown that such coatings can have unexpected properties. For example, energetic ion bombardment is known to cause the production of 'non equilibrium' phases and can extend the normal solubility range. Thus HCP Ti-Al coatings can be deposited which would be expected to have good tribological properties. Properties such as this have been studied and exploited for suitable applications. Further studies showed how parameters such as ion current density are dependant on target current and have a large influence on coating structures and properties. This is all of importance to materials scientists, surface engineers and manufacturers of coating equipment.