The tribological performance and tribochemistry of vacuum deposited nanocrystalline WC/amorphous diamond-like carbon (DLC) composite coatings were investigated. Coating chemistry was varied by regulation of carbon content between 30 and 90 at.%. Deposition temperature was used to adjust the degree of beta-WC crystallinity from near amorphous with 1-3 nm sized grains to nanocrystalline with 5-10 nm sized grains, which were embedded in unhydrogenated DLC matrix. The microstructure critically influenced both the hardness and tribological properties of WC/DLC composites. Coatings with poorly crystallized WC were softer (15 Cpa) and exhibited lower friction and higher wear rates in comparison to harder (26 Cpa) composites with larger WC nanocrystals. The hardness of WC/DLC composites was at least twice as high as the hardness of metal doped DLC coatings reported in the literature. Micro Raman and X-ray photoelectron analysis was performed on transfer films formed on the surface of steel balls in sliding against WC/DLC composites in humid air and dry nitrogen, which found both oxides and graphite carbon, providing self-lubrication. The high hardness and self-lubricating properties of WC composites resulted in low wear rates and friction coefficients of about 0.2. Relationships among coating chemistry, structure, hardness, friction, wear rates, as well as, tribofilm composition and structure are discussed.