What was the name of the Mongol legal code?

The Mongol legal code was called the Yassa. Also written Yasa, Yasaq, Jazag, or Zasag, it was a body of rules and precedents associated with Genghis Khan and later Mongol rulers.

The Yassa appears to have developed from wartime commands and administrative decisions made during the unification and expansion of the Mongol Empire. It addressed military discipline, judicial matters, relations among subjects, and the conduct expected at Mongol assemblies. Genghis Khan is traditionally associated with its creation, while his adopted son Shigi Qutuqu is said to have recorded judicial decisions.

The Yassa was not preserved as one complete surviving legal book. Historians reconstruct it from later accounts, including Persian and other non-Mongol chronicles. Those sources often blur the distinction between yassa, meaning authoritative decrees, and yosun, meaning customary rules. As a result, claims about a detailed, fixed code should be treated cautiously.

The Yassa is not the Justinian Code, which was compiled under the Byzantine emperor Justinian I, nor is it identical to religious law such as the Torah or Sharia. Ögedei later reaffirmed the Yassa as part of Mongol imperial governance.