The use of classroom assessments to enhance teaching and learning is an important issue in contemporary language teaching practice. Meaningful assessment activities help learners see what quality academic work is like and foster dialogue to help them engage independently with feedback. This Introduction discusses a number of dimensions to take account of in assessment for teaching, as well as various approaches to assessment, many of which do not involve tests per se. The paper also discusses Assessment Literacy, the elements of assessment knowledge and practice that language teachers should be aware of as they work to incorporate assessment into their classroom planning. Finally, the five papers in the Special Issue are introduced.