This book provides information on inheritance of color and other traits in koi in an understandable and organized manner. The book was written by a fish geneticist who has performed scientific studies on koi genetics for 25 years and has authored many scientific articles on this subject. To a large extent, the content of this book is based on the results of studies by the author with colleagues. The book also describes how data on the variability of complex color traits in koi are collected and how the inheritance of these traits is analyzed. In the first part of the book the general principles of inheritance are explained. The book is extensively illustrated and contains more than 60 photographs, schemes, graphs and tables. This book would be interesting and useful for koi hobbyists and culturists as well as for anyone who is interested in fish genetics.