Cumulative research within a number of traditions has shown that effective teaching calls for distinctive, identifiable forms of subject-related knowledge and thinking, yet the significance and complexity of such knowledge is not well represented in professional debate and policymaking. This is a particularly pressing issue within mathematics education, given world-wide aspirations to improve quality of teaching and learning in the face of widespread difficulties in recruiting teachers who are conventionally well-qualified in mathematics and confident in the subject. This book, the outcome of two years of collaborative effort, brings together a team of experts in the field of mathematics teacher knowledge to produce an authoritative, ‘state of the art’ exposition and critical commentary on this important and topical domain, including reports of original research in the field. It offers constructive and helpful ways of conceptualising mathematics teacher knowledge in its cultural context, as well as a range of theorised tools to support its improvement.