An Encyclopedia of Tolkien by

Is a comprehensive reference guide to J.R.R. Tolkien's fictional world of Middle-earth. It was written by David Day and was first published in 1979, and an updated and revised edition was released in 2012. The book features over 500 entries on characters, places, and items from the world of Middle-earth, including a detailed timeline and genealogy of the major characters. 

The book also contains illustrations, maps, and photographs to help readers visualize the world of Middle-earth.

The entries in the book are organized alphabetically, and provide detailed information about each character or place. 

The book also includes an introduction to Tolkien's life and works, and a bibliography of his works.

One of the things that I liked the most are the family trees, the chronological guide of events and the graphic art is very well done.

Overall, "An Encyclopedia of Tolkien" is a valuable reference guide for fans of J.R.R. Tolkien's works, and provides a wealth of information about the world of Middle-earth.