This booklet focuses on effective mathematics teaching. Drawing on a wide range of research, it describes the kinds of pedagogical approaches that engage learners and lead to desirable outcomes. The aim of the booklet is to deepen the understanding of practitioners, teacher educators, and policy makers and assist them to optimize opportunities for mathematics learners. Mathematics is the most international of all curriculum subjects, and mathematical understanding influences decision making in all areas of life--private, social, and civil. Mathematics education is a key to increasing the post-school and citizenship opportunities of young people, but today, as in the past, many students struggle with mathematics and become disaffected as they continually encounter obstacles to engagement. It is imperative, therefore, that we understand what effective mathematics teaching looks like--and what teachers can do to break this pattern. The principles outlined in this booklet are not stand-alone indicators of best practice: any practice must be understood as nested within a larger network that includes the school, home, community, and wider education system. Teachers will find that some practices are more applicable to their local circumstances than others.