Since the publication of the first Handbook of Research of Mathematics Teaching and Learning in 1992 and edited by Doug Grouws, research in mathematics education has continued to flourish: moving into new domains, digging more deeply into many enduring questions, and asking new ones. At the same time, mathematics education has continued to mature as a field of study. As the field has matured, there has been growing recognition of the importance of reflecting on what distinguishes the mathematics education research from other fields and on what influences the nature of its activities. During the past dozen or so years, advances in information technology have accelerated the pace of change in society and diverse individuals and groups have begun to promote a variety of old and new instructional approaches, programs, and policies for mathematics education. general, and widespread reform in mathematics education in particular. Researchers are being exhorted to gather and analyze data in support of specific agendas. A pressing challenge for the mathematics education researchers has been to reach out to its constituents and provide research-based advice about questions that concerned that constituent community, and to do so in an unbiased, rational, and convincing manner. several chapters. The Overview will contain chapters on the philosophical, theoretical, and methodological underpinnings of mathematics education research. Section II, on Teachers and Teaching, will contain discussion of research on teacher knowledge, teacher affects and beliefs, teacher education and professional development, and what goes on in classrooms. Section III, on Influences on Student Outcomes, will focus on curriculum, tasks, and materials, teaching practices, race, class, gender and other community and culture influences on student outcomes, and mathematics learning in non-school contexts. thinking in early childhood, whole number operations, place value, and number sense, rational number and proportional reasoning, early and later algebraic thinking, problem solving and modeling, justification and proof, geometry and measurement, probability, statistics, and post-secondary mathematics learning. The chapters in section V, Assessment, will consider classroom assessment, high-stakes assessment, and international and national assessments. The final section, Issues and Perspectives, will offer viewpoints on national and local policy, technology, equity and access, and assessment. This section will close with a view from the outside, prepared by a non-researcher.