I think the best book for understanding horses is “Horse Sense: The Obvious Solutions to All Your Horse Problems” by Linda K. Greene. It is a comprehensive guide that gives you the tools you need to create a trusting, respectful relationship with your horse. It covers a wide range of topics, such as horse health, training, discipline, rehabilitation and nutrition, as well as safety considerations. It also gives practical advice on how to develop communication and trust with your horse. Greene is an experienced horsewoman and trainer, so her advice is well-rounded and based on years of experience. This book is well written, easy to understand, and full of useful information. It's a great resource for anyone who is looking to learn more about horses and develop a strong bond with their horse.