The textbook "Learning to Calculate and Developing Flexibility" offers a comprehensive exploration of the topic of flexible calculation in elementary school. It emphasizes the necessity of promoting flexible calculation skills in mathematics education to support children in moving away from counting-based calculations. The book examines what exactly is meant by flexible calculation and how these skills can be fostered throughout the entire elementary school period for children with different learning backgrounds. It takes both a theoretical and a practical perspective to make the topic concrete for teaching. The authors, Elisabeth Rathgeb-Schnierer and Charlotte Rechtsteiner, provide valuable insights and suggestions for educators to make mathematics instruction more effective and to improve students' calculation abilities.