“Willem de Sitter (1872-1934) was not only one of the most influential astronomers of his time but also a co-author and a correspondent of Albert Einstein. This biography of Willem de Sitter (1872-1934) is comprehensive, very readable, and excellently illustrated. A physicist and a skilled writer wrote the book. It provides a beautiful and understandable description of the physics that was debated by Einstein and de Sitter, in addition to the alternative cosmological model that de Sitter proposed, which became known as the De Sitter Universe. However, this is only a small portion of an incredibly interesting and eventful life story that includes numerous contributions to the field of astronomy in addition to many places and personalities from the early 20th century. All readers who are interested in astronomy, physics, and the history of these fields will enjoy reading this book.”