This book describes an alternative way of presenting mathematical arguments, structured derivations, that aims at making the reasoning more transparent and easier to understand. A structured derivation shows clearly the overall structure of the argumentation, while at the same time requiring that each step in the derivation is carefully justified. Structured derivations can be used in any area of mathematics, and at any level of education. The format has been specially designed for teaching mathematics in a digital environment, with editors for creating solutions to mathematics problems, the web for rapid feedback from teachers, and computers for analyzing the correctness of students solutions, just to name a few examples. The method has been developed in close cooperation with mathematics teachers. It has been tested in a large number of pilot courses on high school level, with very good feedback from both teachers and students.