Book by the famous horsewoman Ingrid Klimke, a mandatory reading book especially if you like young horses, and want to have a good theoretical basis on how to do things
Riding Connected
Fundamental book which will help you improve your saddle and be more in sync with your horse.
The riding of Kottas
Book of the well-known horseman of the Vienna school Arthur Kottas. Very instructive book for lovers of classical horseback riding.
Dressage for all
Book written by famous Spanish rider Víctor Álvarez, has a first part of the book with theory, and the second part talks about reflections on horseback riding.
Reasoned riding
It is a book focused on riding instructors. But in my opinion it is a book for all riders, whether you teach or not. Because you will learn why many of your defects, and how to correct them.
Reiner Klimke
Reiner Klimke tells how his truck to success went with his famous horse Ahlerich. A very inspiring book and very enjoyable to read.