The Ruusan Reformation was a fictional event in the Star Wars universe when the Republic Measures and Standards Bureau reset the year zero to year of the Battle of Ruusan, which is 1,000 BBY by the current date system.

Due to Palpatine's comment in Attack of the Clones that the Republic had only existed for a thousand years (instead of a thousand generations) and that there had been no "full-scale" war for all the Republic's history, the Expanded Universe literature has established that the Battle of Ruusan ended a war with the Sith, the Republic had to be built up from the ground up, making the Ruusan Reformation much more than a simple change of the dating system.

The system of government did not seem to change too dramatically (as the Republic had been ruled by a Supreme Chancellor and Galactic Senate as early as 4,000 BBY), but the Jedi Order underwent a significant adjustment. In symbolic measures, largely to convince the Republic that they would not become a conquering army, the Jedi abandoned their battle armor, renounced all military ranks (such as 'Lord'), disbanded their armies and placed themselves under the supervision of the Supreme Chancellor and the Judicial Department . In order to lessen the chance of a Sith resurgence, the Order began moulding children from birth. In addition, the training of padawans was centralized on Coruscant, to remove the danger of unsupervised students delving into forbidden Sith knowledge.

References

1. Ref. Power of the Jedi Sourcebook.