Interestingly, both Everyman and Gambit, two UK publishers, come out with a book on the Ruy Lopez at the same time. 

The underlying book is a repertoire book for black, centered around a Karpov special, the Zaitsev Variation in the Closed Defence. The Ruy Lopez book by Andrew Greet (from publisher Everyman), is a repertoire book for white based on the Worrall System (5.Qe2) to avoid lines like the Zaitsev. Concludingly they have very little in common. 

The Ruy Lopez (or Spanish Opening) is one of the critical chess battlegrounds. It has long been recommended as an excellent chess opening for training purposes, as it leads to a wide variety of structures and strategies.

This book is a complete guide to handling the black side of the Lopez, based principally around the Zaitsev Variation, upon which Anatoly Karpov relied during much of his career. This line leads to sharp play, often in open battles where Black gains active counterplay and challenges White to seize the initiative on the kingside.

The authors explain in detail how Black can weather the storm. They also explain how Black can handle the practical problem of the Ng5 repetition, and recommend reliable procedures against White's other options in the Lopez, starting off with the Exchange Variation, and moving on to a variety of closed systems.

Throughout, the emphasis is on what readers actually need to know and understand in order to play the opening successfully in practice. There is a great deal of explanation of important ideas, and the authors take pains to guide their readers away from potential pitfalls.