Yisuji 夷俗記 "The customs of the barbarians", also called Beilu fengsu 北虜風俗 "The customs of the northern slaves" (slave being a derogatory term for the steppe peoples) is a book on the Mongols written during the late Ming period 明 (1368-1644) by Xiao Daheng 蕭大亨 (1532-1612), courtesy name Xiaqing 夏卿, style Yuefeng 岳峰, who also wrote a book called Fanfeng jilüe 藩封紀略.
The text, finished in 1594, is divided into 20 brief chapters that inform the reader about the lives, beliefs and habits of the "Tatars" (post-Yuan period Mongols). It describes the compositions of tribes and families, administrative and legal matters, burial and wedding rites, rites and ceremonies of Tibetan Buddhism, taboos and proprieties, the treatment of guests, education, hunting, pasturing, food, clothing and warfare. The book focuses on the Mongol tribes of the Tümed 土默特 and Ordos 鄂爾多斯, both living close to the Great Wall.
The aim of his book was to demonstrate that the Mongols, although militarily strong, were still "barbarians", and that the Chinese could learn what were their shortcomings, in order to become their master. The manuscript version of the book bears the title Beilu fengsu and includes, as an appendix, a genealogy called Beilu shixi 北虜世系.
Henry Serruys (1945) published a study of the text, "Pei-lou feng-sou: Les coutumes des esclaves septentrionaux de Hsia Ta-heng", Monumenta Serica, X: 117-208. An English version of this study was published posthumously by Françoise Aubin (ed.), Henry Serruys, The Mongols and Ming China: Customs and History (London: Variorum ).