The adhesion performance of thin deposited films is of critical importance in many technological applications. These applications include metal/ceramic and metal/polymer structures for semiconductor packaging and contact fabrication, optical coatings on glass, and protective coatings on metals. In many such cases, film and substrate have no bulk chemical affinity. However, strong and stable adhesion has been obtained by means of ion beam treatment to tailor the interface atomic structures for the purpose. We shall review successful application of (i) ion beam mixing of existing interfaces, (ii) ion beam pre-treatment of substrate surfaces prior to deposition and (iii) implantation from various diagnostics including XPS, TEM, Mossbauer conversion electron spectrometry, correlated with adhesion tests, to show how optimum interface tailoring achieves chemical bonding across the interface, preferably with contaminant removal and crack toughening of the interface region. © 1989.