(written from a Production point of view)
The Star Trek Concordance is a reference book written by Star Trek fan Bjo Trimble. The concept for this book, an episode guide beefed out with background information, was based on a privately-printed fandom publication by Los Angeles-based Mathom House Publications, established by Dorothy Jones Heydt in 1969. While the original edition was condoned by the franchise, as a fan production, it was neither officially licensed nor endorsed. In 1976, Ballantine Books chose to release an edition using their Star Trek publication license.
The Concordance cross-referenced episodes, characters, alien species, etc. from both series. Trimble gave animated material equal weight to TOS in this book, and also included fan artwork and illustrations, indicative of its origins as a fandom publication.
Unfortunately there are mistakes throughout the book, especially in the cast lists. These lists were copied to the later editions of the Star Trek Encyclopedia with the errors remaining. This has also led to fan sites listing incorrect information. Some of these errors were corrected in the updated release, along with additional names and corrections from original Desilu and Paramount call sheets.
Contents (first professional edition)
- The Concordance has a special cover featuring an above view image of the saucer of a starship on it, with the secondary hull and nacelles on the back cover. Integrated into the front cover is a turn wheel which could be used to locate any Star Trek episode. As you turn the wheel to the episode you wish to locate, the associated stardate, call letters (abbreviated letters used to identify the episode by) and which page the episode summary can be found.
- "Dedicated to three men who made this book possible: Gene Roddenberry for creating Star Trek in the first place, John Trimble for believing I could get this book together, Martin LeVita for making certain that I did it!" – Bjo Trimble, page 5.
- by Bjo Trimble, pages 8-9.
by Dorothy Jones Heydt, page 10.
- page 11.
- Time Line
- Found on pages 12-13 is the list of episodes organized in order of stardate.
- Found on pages 14-15 is the list of episodes organized in alphabetical order, and the pages their summaries can be found on.
- Fan art
- Found on pages 19-31 includes a number of images created by many known and unknown fans. Fans who contributed include:
- Found on pages 123-255
- Located on page 256, includes an index of episode abbreviations and the pages they can be found on.
- The first fan edition was published in March 1969, and covered the first two seasons of Star Trek: The Original Series. Trimble recounted how the work came to be, "The Concordance started with a young lady taking copious notes on episodes as they were viewed. I started helping her. When she had shoeboxes full of 3×5 index cards, I suggested that we put together a sort of encyclopedia fanzine. But it began to take too long and she lost interest. When we finally produced the Concordance fanzine, I was foolish in giving the young lady all the writing credit, which was not entirely true. For subsequent publications of the book, she had no input at all. John [remark: her husband] and I produced the first fan-published edition on an offset press in our basement. If you purchased a copy and happened to be in town, you had to come to our house to collate your own book!" 
- To many in "Trekdom", Trimble's book was the reference work for all things pertaining to Star Trek until the advent of the works from Michael Okuda, but Trimble did acknowledge that not all fans were of the same mind, "The fan reaction was about the same as anything that happens Trek-wise today: some fans loved the Concordance, others hated it and nitpicked it to death. Some of their criticism was valid, but a lot of it was simply jealousy that they had not thought of the idea. Subsequently, several worked on their own version, but Mike Okuda was the only one who ever gave us credit for our pioneering research into the subject."  Okuda had actually contributed to the expanded versions of Trimble's book, before he embarked on his own. 
- An edited and corrected version followed the same year. The third season was tackled four years later when The 3rd Season Supplement to the Star Trek Concordance was released by the same company, followed by a 24-page "Additions and Corrections to the Star Trek Concordance and Supplement" in 1974. A spin-off 36-page digest-sized coloring book, featuring artwork from the Concordance, was released in 1973.
- The first expanded (to include information pertaining to Star Trek: The Animated Series) professional publication was released by Ballantine Books in 1977 as an unofficial companion to The Original Series and The Animated Series. It was this edition that received a short-lived official endorsement by Paramount Pictures, which was revoked however, when the franchise released its own, similar work, The Star Trek Compendium of 1981.
- The Citadel edition, published in 1995 was updated to include summaries of the first seven movies and key Star Trek: The Next Generation and Star Trek: Deep Space Nine episodes featuring Original Series characters. However, the revised book was published too soon to contain any details from the DS9 episodes "The Sword of Kahless" and "Trials and Tribble-ations", the Star Trek: Voyager episode "Flashback", or Star Trek: First Contact.
- The Citadel edition served as the basis for the slightly abridged UK edition, which was released later the same year by Titan Books.
First book in series
The Star Trek Guide