For several years (about 20) both authors have been working in the domain of Earth rotation, and in particular on nutation. The Working Group on nutation, established by the International Astronomical Union and the International Union of Geodesy and Geophysics in 1994, was a starting point for bringing together scientists thinking about what was missing in the nutation series adopted by the International Astronomical Union. Collaboration between the scientists of the WG was very successful and, in particular, the authors' collaboration began at that time. Recently, it has appeared to us that there were no existing books yet dedicated to the subject, and the scientific community is looking for a suitable publication. The literature contains a lot of relevant articles, but many of them rely on previous work and do not give full details. This book aims at bringing everything together for the first time. The book is addressed to students or scientists who want to understand nutations. The aim of this book is to give a reasonably comprehensive introduction to the fundamental concepts, mathematical formalism, and methodology of the Earth's nutation. It is only assumed that the student or reader is familiar with the elementary principles of calculus, although we might have used in some parts short-cuts for reasons of simplicity, and with the underlying physical principles in the foreground. Another important aim of this book is to make a comprehensive list of the geophysical and astronomical processes involved in nutation, in order to be able to investigate the “next decimal place.”

The authors wish to take this opportunity to acknowledge all those who have aided in the preparation of this book.