You Yu 由余, also called Yao Yu 繇余, was a high minister in the state of Qin 秦 during the late Spring and Autumn period 春秋 (770-5th cent. BCE). He hailed from the nomad tribes of the Western Rong 西戎, or even was a subject of the regional state of Jin 晉 who had fled for political reasons to the land of the Rong.
He occupied a high position in the government of the native king of the Rong and was sent as an envoy to the court of Duke Mu of Qin 秦穆公 (r. 659-621). The Duke had a conversation with You Yu and perceived him as a competent person. You Yu was therefore asked to stay at the court of Qin, but he refused. Liao 廖, chamberlain for the capital (neishi 內史) therefore suggested to the Duke to send to the king of the Rong a group of female dancers that lured the barbarian ruler into a licentious lifestyle. The native king wholly neglected his people and even refused to accept You Yu's admonishions to abstain from wine and women.
You Yu finally decided to give up and offered Duke Mu of Qin his services. He was rewarded with the family name of You 由 and entrusted with the command of an army that was to conquer the land of the Rong. You Yu was appointed senior minister (shangqing 上卿) and was bestowed the land of the Rong as a territory.
There was a book attributed to You Yu that is called You Yu shu 由余書.