The development of key competences for lifelong learning has been an important policy imperative for EU Member States. The European Reference Framework of key competences (2006) built on previous developments by the OECD, UNESCO and Member States themselves. It defined key competences as knowledge, skills and attitudes applied appropriately to contexts. Now most Member States have incorporated key competences, or similarly broad learning outcomes, into their school curriculum frameworks. This is a necessary but insufficient step towards implementation; for the effective development of learners' key competences, assessment must also change. This article focuses on the challenge of assessing cross-curricular key competences in primary and secondary education. It is based on a major study for the European Commission (Gordon, "et al.", 2009), which drew on information gathered and validated with the help of experts in each of the 27 EU Member States. The study's typology of assessment provides a basis for reviewing some recent developments in Member States. Present challenges and innovative responses are addressed, including "unpacking" key competences, "mapping" them to contexts and "accessment" of their full scope and range. Policy developments are considered in the context of the author's work with the European Commission's Thematic Working Group on the assessment of key competences. The article concludes with considerations for policy and practice.