Book excerpt: The aim of this book is to contribute towards literature in the field of mathematics education, specifically the development of 21st century competencies amongst learners of mathematics.The book comprising fourteen chapters, written by renowned researchers in mathematics education, provides readers with approaches and applicable classroom strategies to foster skills and dispositions that will enable learners to thrive in the fast-changing and complex world that we live in today.The chapters in the book can be classified into three broad themes. The first is an examination of what is meant by 21st century competencies and how they can be developed within the context of the mathematics curriculum. The second is an in-depth discussion of evidence-based practices aimed at fostering specific competencies like metacognition and reflective thinking, critical thinking and communication skills. The last and third theme is about teaching approaches that are likely to feature increasingly in the 21st century classroom, for example flipped learning or the use of comics and storytelling.