Xun You (157–c.September 214), courtesy name Gongda, was a statesman who lived during the late Eastern Han dynasty of China and served as an adviser to the warlord Cao Cao. Born in the influential Xun family of Yingchuan Commandery (around present-day Xuchang, Henan), Xun You was recruited into the civil service by the general He Jin. When the warlord Dong Zhuo hijacked and controlled the Han central government between 189 and 192, Xun You plotted with four others to assassinate him but was discovered and imprisoned. Following his release after Dong Zhuo's death, he wanted to serve as the Administrator of Shu Commandery (around present-day Chengdu, Sichuan) but eventually settled as an official in Jing Province.

In 196, after Cao Cao received the figurehead Han sovereign, Emperor Xian, and reestablished the new imperial capital in Xu (許; present-day Xuchang, Henan), he summoned Xun You to the capital to serve as a Master of Writing and Military Adviser. From then on, Xun You was simultaneously a Han statesman and a subordinate of Cao Cao. He accompanied Cao Cao on his military campaigns as a tactical adviser and occasional commander. Between 198 and 207, he advised Cao Cao in the battles against rival warlords such as Zhang Xiu, Lü Bu, Yuan Shao and Yuan Shao's successors. In 207, on Cao Cao's recommendation, Emperor Xian made Xun You a village marquis to honour him for his contributions. In 213, after Cao Cao had been enfeoffed by Emperor Xian as the Duke of Wei, Xun You served as the Prefect of the Masters of Writing in Cao Cao's dukedom. In 214, while accompanying Cao Cao on a campaign against the southern warlord Sun Quan, Xun You died of illness along the way. Described as a highly profound and insightful thinker, Xun You was also known for keeping a very low profile and his discretion.

The authoritative historical source on Xun You's life is his official biography in book 10 of the Records of the Three Kingdoms (Sanguozhi), which was written by Chen Shou in the third century.

In the fifth century, Pei Songzhi annotated the Sanguozhi by incorporating information from other sources to Chen Shou's original work and adding his personal commentary. Some alternative texts used in the annotations to the Sanguozhi include: the Wei Shu (魏書; Book of Wei), by Wang Shen (王沈), Xun Yi (荀顗) and Ruan Ji; the Xun Shi Jia Zhuan (荀氏家傳; Xun Family Genealogy); the Han Ji (漢紀; Annals of Han), by Zhang Fan (張璠); the Fu Zi (傅子), by Fu Xuan.

Xun You was born in the influential Xun family, whose ancestral home was in Yingyin County (潁陰縣), Yingchuan Commandery (穎川郡), which is in present-day Xuchang, Henan. His grandfather, Xun Tan (荀曇), whose courtesy name was Yuanzhi (元智), served as the Administrator (太守) of Guangling Commandery (廣陵郡; around present-day Huai'an, Jiangsu). Xun You's father, Xun Yi (荀彝), served as a commandery-level Assistant Officer (從事). Xun Yi was a second cousin of Xun Yu, hence Xun You was Xun Yu's second cousin-nephew even though he was six years older than Xun Yu.

Xun You was orphaned at a young age. He was probably raised by his uncle Xun Qu (荀衢) and his grandfather Xun Tan. When his grandfather died, a minor administrative assistant, Zhang Quan (張權), offered to be the tomb keeper. Xun You, who was 12 years old then, sensed that something was wrong. He told his uncle Xun Qu, "This man looks suspicious. I believe he's up to something." Upon investigation, it was revealed that Zhang Quan was actually a murderer on the run. Because of this incident, the young Xun You was seen as an extraordinary boy. When Xun You was six or seven, Xun Qu once accidentally injured him while he was drunk. Since then, every time Xun You left or entered his home, he would do so at times to deliberately avoid meeting his uncle. Xun Qu was very surprised by his nephew's intelligence when he heard about it.

When He Jin rose to power in 189 and became regent to his nephew, the young Emperor Shao, he recruited over 20 notable members of scholar-gentry background to join him including Xun You, who had been noted by the famed judge of talent Yin Xiu (陰脩). He was appointed as a Gentleman of the Yellow Gate (黃門侍郎), allowing him to act as a liaison to the palace, in the imperial capital, Luoyang and would be the person fellow recruit Zheng Tai would complain to . However, within the same year, He Jin was assassinated by the eunuch faction he had sought to destroy. The warlord Dong Zhuo took advantage of the ensuing political turmoil to hijack and control the central government. Between 190 and 191, several regional warlords formed a coalition and launched a campaign against Dong Zhuo in the name of saving the emperor, in response Dong Zhuo ordered Luoyang to be burnt down and relocated the capital to Chang'an. In Chang'an, Xun You secretly plotted with Zheng Tai (鄭泰), He Yong, Chong Ji (种輯) and Wu Qiong (伍瓊) to assassinate Dong Zhuo, who was notorious for his cruelty and tyranny. However, they were discovered and Xun You was arrested and imprisoned. While he was incarcerated, Xun You spoke and behaved normally as though nothing had happened. He was only released after Dong Zhuo was killed in 192. However, the Wei Shu mentioned that Xun You was released after he sent someone to persuade and convince Dong Zhuo to free him.

Xun You then resigned amidst the chaos resulting from Dong Zhuo's assassination and fled home. Appointed to be the Chancellor (相) of Rencheng State (任城; southwest of present-day Zoucheng, Shandong), he rejected this appointment and asked to be the Administrator (太守) of Shu Commandery (蜀郡; around present-day Chengdu, Sichuan) because he heard that Shu Commandery was prosperous and situated in a geographically strategic location. However, he was unable to travel to Shu Commandery as the routes to Shu had been cut off in the chaos, choosing instead to stay in the relative stability of Jing Province.