About Sixty: Why Every Sherlock Holmes Story is the Best edited by Christopher Redmond.
The Apocrypha of Sherlock Holmes by Leslie Klinger.
Arthur and Sherlock: Conan Doyle and the Creation of Holmes by Michael Sims. Review by The Guardian.
The Encyclopaedia Sherlockiana by Jack Tracy. Reference book about names, places and Victorian details in the stories, published 1977 in hardback. Paperback edition also available.
From Holmes to Sherlock: The Story of the Men and Women Who Created an Icon by Mattias Boström. Reviews by The Washington Post and New York Journal of Books.
The Philosophy of Sherlock Holmes (Philosophy of Popular Culture) by Philip Tallon
The Sherlock Holmes Book (Big Ideas Simply Explained) by Leslie S. Klinger.
The Sherlock Holmes Companion by Daniel Smith.
A SherlockHolmes Handbook by Christopher Redmond.
The World Bibliography of Sherlock Holmes and Dr. Watson, by Ronald B. De Waal, published 1974. Additional volume: The International Sherlock Holmes, 1980. New edition, The Universal Sherlock Holmes, in five volumes, limited edition, 1994.