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The trends in the use of hard protective coatings in WC–Co metal cutting inserts are reviewed in light of recent evaluations of mechanical and structure-sensitive properties such as elevated temperature microhardness, microfracture toughness, and internal stress. A better understanding of the role of hard coatings has evolved due to development of reliable methods to measure mechanical properties of thin coatings (of the order of 5 μ thick). There are intrinsic differences in the microstructure and residual stress state of chemical and physical vapor deposited (CVD and PVD) hard coatings. High compressive residual stress and fine grain size in PVD coatings contribute to increased microhardness and microfracture toughness. However, these benefits are reduced at high temperatures. Certain well-known structure/property concepts in bulk materials are shown to be applicable to hard coatings, which aid in interpretations of metal cutting wear behavior.