This chapter addresses the use of Computer Algebra Systems (CAS) for mathematics education in summative as well as formative assessment situations, and the ways in which CAS alter or augment these. The chapter draws on carefully selected illustrative examples from secondary school, upper secondary school and university level in Denmark, Germany, and the United Kingdom. The theoretical approach for developing the discussion draws on constructs related to assessment in general, assessment (both summative and formative) involving CAS as well as the theories of instrumental genesis and instrumental orchestration.