I bought this book to help with a dissertation I was writing on the evolution of play in humans and primates. I have found it to be enormously helpful. Burghardt writes clearly and concisely, in a plain style, and his book is very well-structured; it is easy to follow his train of thought. He starts by giving an account of the various theories of play and the various forms of play, and wisely devotes an entire chapter to laying out a useful and relevant definition of what constitutes play - as anyone who has read up on the subject will know, this is no easy task. He then moves on do discuss play in mammals, birds, reptiles, and invertebrates, in search of the most primitive animals that play, in order to investigate the evolutionary roots of this behaviour. As an undergraduate student, I found his discussions easy to understand, and his many examples were very useful; I also think that a more advanced reader would find much that was useful in this volume. It is to be strongly recommended to anyone beginning to learn about animal play, and contains some discussion which is very relevant to human play as well. It is also generally free of some of the personal acrimony which comes through in some other books on the subject; this seems to be a contentious area of academia! I would like to make one criticism of this book: while there is an extensive author index, species index, and list of references, the subject index is sadly limited. In a book of just over 400 pages, it becomes very difficult to keep track of the many subjects discussed, and such a small index really limits the book's ease of use as a reference text. If there is a further edition of this book, I would strongly recommend that the index be extended.