The articles in this Special Issue arose originally from the work of the Research Forum on Sociological Frameworks in Mathematics Education Research at the conference of the International Group for the Psychology of Mathematics Education (PME) in 2009. The acceptance of this Research Forum at PME was indicative of the shift within mathematics education research during the last two decades involving what has been called the “social turn” (Lerman, 2000). Researchers concerned with a wide variety of issues within mathematics education have come increasingly to see the inseparability of culture, context and cognition. Even within research that focuses primarily on cognitive aspects of learning and knowledge, notions of situated learning and distributed knowledge (Lave & Wenger, 1991) are widely used, as well as other theoretical perspectives that emphasise social aspects of learning, drawing in particular on Vygotskian psychology (Vygotsky, 1978). Moving beyond seeing mathematics learning solely as the endeavour of individual students and teachers has been reflected in a broader conceptualization of the subject matter of the field of mathematics education research. Valero (2010) has drawn our attention to the complexity of the networks of communities, interest groups and practices relevant to mathematics education and to the need for research to address this multiplicity of social practices and the connections between them. We are thus aware of the importance of studying the various communities and practices in which students and teachers participate, both within the classroom and beyond. We recognise the influence of policy and institutional structures and constraints at local, national and international levels. We appreciate the impact of the various discourses available inside and outside the school—discourses in the sense written with a capital D by Gee (1996 )a nd defined as incorporating “theories” about what is normal and right and structuring the kinds of identities available to participants. This increasing attention to social aspects of learning has been accompanied by a growth in research foregrounding issues of social justice. Differing levels of achievement in mathematics in particular as well as in education as a whole have been associated with membership of various social groups and the effects of such factors as gender, ethnicity, class and linguistic background on the achievement of students in school mathematics have long been a focus of study. However, our ways of understanding the phenomenon of school failure have developed. In particular, there has been a move from locating the reasons for failure in the characteristics of the individuals concerned or of their communities towards seeking to understand how the