“…The différences between contributions of different authors may concern the mathematical approach (queueing theory, renewal theory, dynamic programming,...), the degree of knowledge of the system state (préventive maintenance model, preparedness model, inspection model) or different aspects of the problem (minimal repair model, shock model, miscellaneous replacement model). Références can be found in three major surveys which cover the last forty years of scientific production: MeCall [1] (up to 1964), Pierskalla and Voelker [2] (up to 1975), Valdez-Flores and Feldman [3] (up to 1989).…”