This Handbook provides guidelines to manage obsolescence of Materials, Mechanical Parts and Processes (in-house and sub-contracted). It is useful for any actor of the European Space sector. It covers Materials, Mechanical Parts and Processes (MMPP) used in flight hardware as well as ground support equipment (including test systems) and materials or tools used during process (not in the final product) and skills (know-how). It is not within the scope of this Handbook to address EEE components and software. This document describes the general causes of obsolescences and introduces the concepts of proactive and reactive obsolescence management, depending of the programme phase.