The state of the art concerning the deposition of thick, well-adherent cubic boron nitride films for tribological applications and protective coatings is critically reviewed. It is shown that a great deal of the processes developed up to now for the deposition of thick c-BN films-although they must be considered as major breakthroughs towards the development of a c-BN technology-is not compatible (in terms of substrates, process conditions, etc.) with the requirements of such applications. It is shown further that the peculiarities of c-BN film growth, namely the so-called nucleation sequence and the strong ion bombardment necessary to nucleate and grow c-BN, present serious challenges on the way towards thick c-BN films. The three most important problems, the high stress of the films, their poor adhesion, and their poor stability are addressed, and possible measures to solve them are discussed. Finally, a route is proposed that may lead to the deposition of thick, well-adherent c-BN films. (C) 2007 Elsevier B.V. All rights reserved.