"The book is a valuable contribution to this particular area of group theory. In addition to covering key results and techniques, it points towards a broad range of recent results and open problems." - Benjamin Klopsch
How many groups of order n are there? This is a natural question for anyone studying group theory, and this Tract provides an exhaustive, connected, and up-to-date account of research into this question spanning almost fifty years. Written for graduate students and established research workers alike.