W-Ti-N films were deposited by reactive DC magnetron sputtering from a W-Ti (30 at.%) target, in a mixture of argon and nitrogen at a total pressure of 0.5 Pa, onto steel and silicon substrates. The crystal structure, microstructure, composition, micro-hardness and residual stress were studied as a function of the partial pressure of nitrogen. Films containing less than 30 at.% nitrogen were composed of a mixture of b.c.c. W and f.c.c. W2N phases, while only the f.c.c. phase, probably WxTi1-xNy, was present in the films with a nitrogen concentration of [N] greater than or equal to 36 at.%. The microhardness of the W-Ti-N films increased with increasing nitrogen concentration from 25 GPa for [N] = 0 up to a maximum of approximately 65 GPa at [N] = 25 at.%. This was accompanied by increasing microstrain, while the compressive residual stress remained in the range of 1.3-2.3 GPa. The single-phase W-Ti-N films, with [N] greater than or equal to 36 at.%, exhibited a micro-hardness of approximately 40 GPa and a large compressive stress of, at most, approximately 5.7 GPa at [N] = 40 at.%. The maximum microhardness was found in films that simultaneously possessed: (i) the presence of two crystalline phases; GO large microstrain; and (iii) relatively low compressive residual stress.