The Yamana clan (山名氏 Yamanauji) was a Japanese samurai clan which was one of the most powerful of the Muromachi period (1336-1467); at its peak, members of the family held the position of Constable (shugo) over eleven provinces. Originally from Kōzuke province, and later centered in Inaba province, the clan claimed descendance from the Seiwa Genji line, and from Minamoto Yoshishige in particular. They were valued retainers under Minamoto no Yoritomo, and counted among his gokenin.
The Yamana were among the chief clans in fighting for the establishment of the Ashikaga shogunate, and thus remained valued and powerful under the new government. They were Constables of five provinces in 1363, and eleven a short time later. However, members of the Yamana clan rebelled against the shogunate in 1391 and lost most of their land. Yamana Sōzen, likely the most famous member of the clan, would regain these lands in 1441. Through all of this the clan managed to somehow retain a great degree of reputation and power within the shogunate government; along with the Hosokawa and Hatakeyama clans, they served as agents of the shogunate in resolving various disputes.
Sōzen would then become embroiled in a conflict with Hosokawa Katsumoto over naming the shogun's successor; this conflict grew into the Ōnin War, which destroyed much of Kyoto, and led to the fall of the shogunate and beginning of the Sengoku period. In the end this cost the Yamana much of their former influence and land. By the end of the 16th century, the Yamana had been reduced to holding the better part of Inaba Province. That area would be retained by the Yamana even until the end of the Edo Period.