Mathematics education research as a discipline is situated at the confluence of an array of diffuse‚ seemingly incommensurable‚ and radically divergent discourses. Research claims that have grown out of mathematics education are wide-ranging and antagonistic rather than circumscribed by hidebound disciplinary frames. While there has never been a unified‚ totalising discipline of knowledge labelled 'mathematics education research'‚ and while it has always been a contested terrain‚ it is fair to say that the master paradigm out of which this field has been generated has been that of cognitive psychology. Mainstream mathematics education knowledges refracting the master discourse of psychology —whereby cognition serves as the central privileged and defining concept— clearly delimits its possibilities for serving as a social tool of democratic transformation. The central point of departure of this new collection is that mathematics education research is insufficiently univocal to support the type of uncompromising interpretation that cognitive psychologists would bring to it. The hallmark contribution of this pathbreaking volume edited by Paola Valero and Robyn Zevenbergen is the paradigmatic shift the authors have effected in the field of mathematics education research‚ taking up a position at the faultline of socio-cultural analysis and critical pedagogy.