Diamond films were chemically vapor deposited (CVD) on titanium, tungsten, molybdenum, copper and aluminum oxide substrates. In these studies, the interface formed between diamond and the substrate was exposed by mechanically deforming the metal substrate or diamond film to cause film delamination. The observed degree of adhesion for these interfaces can be ranked in the order: Ti >> Al2O3 (thin films) > Cu > W >> Mo. For highly adherent films, delamination procedures were carried out under controlled conditions in order to preserve the integrity of the interfacial species. The exposed interfaces were characterized by X-ray photoelectron spectroscopy (XPS), scanning Auger microscopy (SAM), scanning electron microscopy (SEM) and Raman microprobe spectroscopy. We find that substantial interfacial reaction layers exist at all interfaces except in the diamond-copper system and are composed of both oxides and carbides of the native substrate. Variations in the relative concentration of these species and the distribution throughout the reaction layer also were observed for the different substrates. We believe that both the chemical composition and morphology of the interface influence the adhesion properties of the diamond coating. Correlated investigations of the interfacial surfaces reveal that fracture of the diamond-metal interface occurs discretely at the diamond nucleation plane or within a reaction layer near the diamond interface. We discuss each of these findings in light of qualitative observations of adhesion and suggest avenues for improving the adhesion of diamond films.