This document describes the generic requirements, criteria and contents of maintenance engineering. This includes guidance on methods and techniques which are used to sustain the required functions of items at any stage of their life cycle. This document gives guidance on how maintenance engineering can contribute to the assurance of required integrity, safety, reliability, maintainability and availability to achieve a sustainable balance between performance, risk and costs. This document does not give guidance on how to set up systems and infrastructure to support the maintenance engineering function. This document refers to standards that further describe detailed methods and techniques. NOTE: The overall maintenance process and management is covered by other CEN/TC 319 standards EN 17007 [10] and prEN (WG 8).