The Three Huan families Sanhuan 三桓 were three lateral lines of the house of Lu 魯 during the late Spring and Autumn period 春秋 (770-5th cent. BCE). Theirs ancestors were sons of Duke Huan 魯桓公 (r. 712-694), hence the term "Three (descendants of Duke) Huan".
The sons of Duke Huan were Gongzi Qingfu 公子慶父 (gongzi means "ducal son", or "prince"; ancestor of the Zhongsun family 仲孫, later called Mengsun 孟孙, family name Meng 孟), Gongzi Ya 公子牙 (ancestor of the families Shusun 叔孫 and Shuzhong 叔仲), and Gongzi You 公子友 (ancestor of the Jisun family 季孫, family name also Ji 季).
The members of these three noble families occupied high positions in the government of Lu, and especially the heads of the Jisun family acted as regents for the dukes.
In 562, it is said, the Three Huan families factually "split up" the power of the dukes by creating their own armies and residing in their own fortified palace compounds. The family Jisun introduced a new system of land tax in their domain, while the family Shusun continued relying on the corvée labour delivered by the peasant serfs. The family Mengsun seems to have relied on both systems for their financial support.
In 537, the domain of Lu was again divided, this time in four parts, of which the family Jisun occupied two. From that time on the regular field tax (tianfu 田賦) was used by all Three Huan families. The dukes Zhao 魯昭公 (r. 542-510) and Ai 魯哀公 (r. 495-467) tried eliminating the usurpatious lateral lines, but without success.