This volume was written primarily for teachers who have developed (or who are being encouraged to develop) an awareness of and commitment to teaching mathematics for understanding. The research findings presented in these chapters suggest instructional implications worthy of these teachers' consideration. Often, the authors in this volume describe instructional practices or raise issues that have the potential to broaden views of teaching and learning mathematics. These chapters provide interesting problems and tasks used in the authors' work that readers can use in their own classrooms. The volume can also be used with courses for preservice and inservice teachers, collaborative teacher study groups, and other professional activities. A hallmark of good research is its connection to the relevant literature in the field, and the authors of this volume have themselves drawn from the research literature to inform their work. The reference lists accompanying these chapters can be useful resources and should not be overlooked. Most importantly for teacher education, this volume showcases the variety of ways teachers can become engaged in research, and we hope that readers will recognize that teacher research can be both accessible and beneficial in the preparation and professional development of teachers. This is not to suggest, however, that this volume is intended only for teachers and teacher educators. It is also intended to be an interesting, informative resource for other researchers, school administrators, and policy makers. The research presented in this volume is intended to provide an opportunity for those outside the classroom to gain insight into the kinds of issues that matter to teachers, the ways in which those issues might be researched, and the contributions that classroom research makes to mathematics education.