The primary aims of the study are to report the state of the art in the area of mathematics teacher collaboration with respect to theory, research, practice, and policy; and to suggest new directions of research that take into account contextual, cultural, national and political dimensions. Because there are different ways of understanding teacher collaboration and its characteristics, enablers, and consequences, the Study will include multiple theoretical perspectives and methodological approaches. We encourage contributions that report research using a variety of methodological approaches including large-scale experimental and descriptive studies, case studies, and research approaches characterized by iterative or cyclical processes such as design research and action research. We also solicit contributions from teachers as well as researchers, to ensure that teachers’ voices are given prominence in accounts of their learning.