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 them. The chapter draws on carefully selected illustrative examples from secondary school, upper-secondary school and university levels 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 and the theories of instrumental genesis and instrumental orchestration.