This monograph outlines the scope of Genghis Khan's law code, the Yasa, which survives only in quotations and references. In so doing, Vernadsky adds to the conventional Arabic sources on the Yasa by consulting the Syriac polymath Barhebraeus, and the Life of the Conqueror of the World by the Persian Juwaini, both of whom mention Genghis' laws extensively. After a comprehensive survey of the known enactments by subject, Vernadsky concludes that the Yasa was not a compilation of Mongol traditional law, but a set of provisions extending it to a multinational empire.