In this chapter, we focus on assessing computational thinking. To do so, we answer questions such as what does computational thinking look like when we look at student performance? How can we identify computational thinking across subjects? What considerations should be made when developing computational thinking assessments? We also discuss what teachers must know in order to assess students’ abilities to think computationally. The chapter reviews different approaches to the assessment of computational thinking and discusses how assessment can inform learning and teaching practices. Finally, we discuss to what extent new forms of assessment require new teacher competencies.