Heqin , or marriage alliance, refers to the historical practice of Chinese emperors marrying princesses, usually members of minor branches of the royal family, to rulers of neighbouring states. It was often adopted as an appeasement strategy with an enemy state that was too powerful to defeat on the battlefield. The policy was not always effective. It implied an equal diplomatic status between the Chinese emperor and the foreign ruler. As a result, it was controversial and had many critics.
Lou Jing (, later granted the royal surname Liu), the architect of the policy, proposed granting the eldest daughter of Emperor Gaozu of Han to the Modu Chanyu of the Xiongnu. His proposal was adopted and implemented with a treaty in 198 BCE. Wang Zhaojun, of the Han dynasty, and Princess Wencheng, of the Tang dynasty, are among the most famous heqin princesses. Heqin was never again practiced by any Han Chinese dynasty after the Tang.
The 20th-century scholar Wang Tonglin praised heqin for facilitating the "melting of races" in China.