Diamond, diamond-like, and their composites (with TiC, TiN, and AlN for diamond, and Cu, Ag, Ti, and Si for diamondlike carbon) have extremely desirable chemical, electrical, and mechanical properties. These corrosion- and erosion-resistant coatings have a wide variety of applications, ranging from biomedical device coatings to packaging of microelectronic devices. However, many of these applications are limited by the poor adhesion of these films to metals, ceramics, and polymers. The adhesion of a film is determined primarily by internal stresses in the film, thermal and lattice mismatch, and most importantly by interfacial bonding. We have developed methods based on mechanical interlocking, chemical bonding, grading of interatomic potentials, and the multilayer discontinuous thin films approach to control stresses and strains in thin films. A substantial improvement in adhesion and wear properties is obtained by using these methods selectively. We review issues related to the adhesion of diamond, diamond-like carbon, and composite films on metal, polymeric, and ceramic substrates.