The present handbook is provided to support the implementation of the requirements of ECSS-E-AS-11 to space projects. With this purpose, this handbook provides guidelines on the way to assess the maturity of a technology of a product in a given environment, to use the TRL assessment outcome in the product development framework, and to introduce some further refinements for specific disciplines or products to which the TRL assessment methodology can be extended. The concept of Manufacturing Readiness Level (MRL) is not addressed in this document, whilst the concept of TRL can be applied to the technology-related aspects of manufacturing.