The Dune Encyclopedia - Willis E. McNelly Fortunately, this work was compiled before Brian Herbert began that truly awful continuation of his father's masterpiece (overall, there were some pretty weak entries in Herbert pere's oeuvre, let's be honest).

It pretends to be a collection of select finds from the Rakis Hoard, discovered 2 millennia after Leto II's death, and there's a wealth of fascinating material that brings a richness and depth to the Corrino and Atreides Imperia. For example, there are biographical entries for all of the major characters of the series. Sometimes more than one - Paul gets three entries, one of which is the highly edited version produced under the God Emperor.

There are also entries that explain the Holtzman Effect, which produced both the personal shield and the means for FTL travel. There's a history of the Bene Gesserit that can be read as an accurate portrayal of a matriarchal cabal that has existed since the Neolithic or as the self-serving chronicle of an organization that can trace its origins to the Butlerian Jihad. There's an explanation of Imperial administration and the Great Convention that governed human affairs for 10 millennia; the origins of Mentats and Sardaukar; an exploration Fremen poetry; the role of the Missionaria Protectiva; a rundown of Duncan Idaho and the gholas who served the Atreides for 3,000+ years; and a furtive look at the vile Bene Tleilax and their face dancers.

There's also a fascinating essay (supposedly one of the few writings that can be attributed to Paul Maud'dib) about the origins, purpose and influence of the Orange Catholic Bible.

Overall, a wonderful companion to the Dune series (though I wish it could have incorporated some of the material from the later books, particularly the Honored Matres).