The Great Holocron was an ancient, dodecahedral holocron.
Housed in the Jedi Archives on Coruscant, the Great Holocron was the centerpiece of the Jedi Temple's library holdings. It contained vast amounts of information that was accessible to any Force-sensitive being willing to open itself to the holocron, and Jedi trainees were encouraged to explore its contents. Despite its ease of access, consumption of its manifold mysteries was thought to be impossible—even Master Yoda was thought, by Archives Director Jocasta Nu, to still struggle with its depth.
While the Great Holocron was designed to only reveal information that its user was prepared to encounter, inexperienced Padawans accessed the Great Holocron under the watchful eye of the Archives Director who stood ready to step in if the young Jedi was drawn in too far.
It was eventually rediscovered by the New Jedi Order in 40 ABY and placed in the library of the Ossus Academy under the care of Master Tionne Solusar. She was not sure whether it was the real Great Holocron or a well-crafted replica.  She would update the Holocron with data from recent eras to continue the work of former archivists before her. 
Topics included basic and advanced lightsaber construction methods, Galactic Republic history, philosophy, Sith history, lightsaber combat, and Jedi techniques. The Great Holocron also included discussions on the dark side of the Force and methods to resist its call.
During the course of the Order's history, many Jedi contributed various scraps of information. Some of the stories and journals submitted are as follows:
- Arca Jeth on the Freedon Nadd Uprising
- Brief mentions of the Battle of Ruusan.
- Obi-Wan Kenobi's recount of his meeting with the Sith Lords, Darth Maul and Darth Tyranus.
- Sar Agorn's view on manipulating the Force.
- Saesee Tiin's speech to a group of younglings on telepathy. Also Tiin's report on the Scimitar.
- Dooku on lightsaber combat, conquering arrogance, his resignation from the Order, and a protest to the Council after the events of the Battle of Baltizaar.
- Yoda on farsight and the Chosen One.
- Tholme on the dangerous aspects of psychometry; using the example of Padawan Quinlan Vos.
- Oppo Rancisis on Malacia.
- Yaddle on Morichro.
- Plo Koon on Electric Judgement and the Mission to Metellos.
- Kit Fisto on waterproofing lightsabers.
- Ki-Adi-Mundi's report of the death of Sharad Hett.
- Cin Drallig on the seven forms of lightsaber combat.
- Mace Windu on Vaapad and the origin of the Korunnai; although the latter entry may have been propaganda by the Galactic Empire.
- Rekpa De on victory and defeat.
- Danzigorro Potts reporting the death of Xendor.
- Vima Sunrider on Ulic Qel-Droma's redemption.
- Tolaris Shim on the four stages of the dark side.
- Deesra Luur Jada regarding the time during and following Revan's reign.
- Reidi Artom's report on the Cularin system.
- Lanius Qel-Bertuk in reference to the Sith Temple on Almas.
- Little information on the Chu'unthor.
- References to the Prophecy of the Chosen One.
- Siri Tachi's observations of Anakin Skywalker.
Behind the scenes
Although not seen in the film, during production of Attack of the Clones, the film's prop-makers made three holocrons for its Visual Dictionary: a Jedi holocron, a Sith holocron, and the Great Holocron.
- Star Wars: Attack of the Clones: The Visual Dictionary
- Star Wars: The Complete Visual Dictionary
- Star Wars: The Ultimate Visual Guide
- Jedi vs. Sith: The Essential Guide to the Force
- The Complete Star Wars Encyclopedia
- Star Wars: The Ultimate Visual Guide: Updated and Expanded