Validation of non-formal and informal learning has been gaining political momentum in Europe within the implementation of lifelong learning policies since the early 2000s. Policy documents claim a variety of education, socio-political and economic benefits from the implementation of validation, making validation a "hero" for lifelong learning. This article discusses the concept of validation of non-formal and informal learning and provides an overview of the different "faces" and interpretations of validation. Starting with the terminology, the article discusses related terms such as recognition, prior learning, assessment, accreditation or certification and their different connotations. Principles and aspects that characterise the current use of validation as a policy priority in Europe are presented. The article highlights the major themes on validation and their implications for policy and research.