The phenomenon of indentation in coated substrates was checked by applying conical and spherical indenters of various geometries in a wide load range. Microscopic observation and cross sectioning of the indentations revealed three concentric regions: the inner contact zone, the indentation crater, and the debonding zone. The latter is formed if insufficient adhesion between the film and substrate gives way to the normal tensile stress on the interface, outside the contact area. In the contact zone the film is permanently compressed, and the indentation, accompanied by sinking in, is fundamentally a plastic deformation phenomenon. An analytical method is presented for estimating the “hardness” (defined as load per indentation crater area) of coated substrates from indentation and deflection measurements of the uncoated substrate plus a single deflection measurement of the coated substrate. Hardness curves (hardness versus force curves) for various indenters are plotted and compared.