Curriculum materials and the interaction with these materials and resources is central in teacher education and professional development. How teachers use and learn from materials fundamentally depends on the interactions between three components: the reader, the material and the context. Teachers' use and learning from text-based materials depends to a large extent on the characteristics of the materials, on the teaching activity in which the teacher is engaged, teachers' beliefs and knowledge, and how these are aligned with the curriculum. What kinds of curriculum materials do teachers select and use, and how? How do teachers learn from these materials, and in which ways do they 'tailor' them for their use and pupil learning? These factors interact in complex ways, as teachers select, interpret and shape the materials, individually and collaboratively with groups of colleagues. The characteristics of the resources shape the teacher's activity; analysing these characteristics enlightens the mathematics presented to the students, and more generally the classroom practice and the development of teacher professional knowledge. The purpose of this book is to provide a wider perspective on this issue in the field of mathematics education. It studies curriculum materials and their uses, in addition to investigations of teacher adaptation and use of those materials, and pays particular attention to digital resources. Teacher's professional activity is studied as a whole, at different moments and in different contexts, in-class and out-of-class, with a variety of agents. The collective dimensions of this activity, the role of a variety of collectives for teachers professional development, constitute a major focus of the work presented here.