The Rule of Two is an essay that concerns a doctrine of the same name. This doctrine was created by the Sith's Dark Lord known as Darth Bane sometime after the Seventh Battle on Ruusan. This essay became the foundation of Bane's re-established Sith Order and was handed down within the Sith Archives from master to apprentice. Later, it was incorporated into Darth Sidious's Book of Sith following the conclusion of the Clone Wars.
In the year 1000 BBY, the Brotherhood of Darkness, which was a Sith organization established and headed by Lord Skere Kaan, suffered defeat at the hands of the Jedi Order during the Seventh Battle on Ruusan. Darth Bane, being the last remaining Dark Lord, made the decision to reform the Sith into a new order. Within this new order, the practices of the Brotherhood were superseded by his own unique system, known as the Rule of Two. To establish his ideas, Bane penned The Rule of Two, a source book that detailed his Sith philosophy of the same name.
This very document was kept safe in the hidden Sith Archives and was passed along from master to apprentice for many centuries. As the Galactic Republic neared its end, the document came into the possession of Darth Sidious, the Sith identity of the politician Palpatine. Following the commencement of the Clone Wars in 22 BBY, The Rule of Two was given to Count Dooku, a former Jedi Master who had turned into Sidious' apprentice under the name Darth Tyranus. He then shared the text with Quinlan Vos, a Kiffar Jedi Knight, hoping to corrupt him. Vos added numerous notes in the margins.
After the Clone Wars ended in 19 BBY, Darth Sidious put together a number of important Sith texts into his Book of Sith, and he made sure to include Bane's text as one of its sections. It should be mentioned that Sidious also added his own handwritten notes across the pages.

- Power of the Sith
- The Mistakes of Ruusan
- The Title of Darth
- Striking from the Shadows
- Selecting an Apprentice
- The Revenge of the Sith
- Personal Combat
- Lightsaber Construction
- Sith Lightsaber Variants
- Lightsaber Combat
- Using the Saberstaff
- Sith Armor
- Dark Side Combat