Crystallographers have to apply many mathematical methods in their daily work. If ever they have a problem, this book will help to solve it. The newcomer starting work will learn how to apply these tools, the practicing crystallographer will find all the data and background material he wants to look up. In the decade since the first edition was published, new things have happened that required revision beyond correction of errors. Two chapters have been added: a section on the projection matrix and another on fast Fourier Transform. The author collected the information during his professional career. The success of the first edition indicates that many other practicing crystallographers just need exactly that information.