This book covers the elementary school mathematics curriculum common in most parts of the world. Its aim is to serve educators (teachers and parents) as a guide for teaching mathematics at elementary school level. The book focuses both on content knowledge and on pedagogical content knowledge. It bridges the gap between fundamental mathematical principles and good teaching practices. It also offers the reader a glimpse on how mathematicians perceive elementary mathematics and presents ideas for specific mathematical activities.The author is also a co-founder of Matific, an adaptive game-based teaching and learning tool for primary school mathematics. Independent studies have shown Matific to improve test scores, reduce maths anxiety, and increase motivation. Matific is available in 26 languages and aligned to mathematics curricula in 46 countries. Awards include Best Mathematics Instructional Solution, Best Game-Based Curriculum Solution and Best Educational App.