The Ogasawara clan (Japanese: 小笠原氏, Hepburn: Ogasawara-shi) was a Japanese samurai clan descended from the Seiwa Genji. The Ogasawara acted as shugo (governors) of Shinano Province during the Sengoku period (c. 1185–1600), and as daimyō (feudal lords) of territories on Kyūshū during the Edo period (1600–1867).

During the Kamakura and Muromachi periods, the clan controlled Shinano province, while related clans controlled the provinces of Awa, Bizen, Bitchū, Iwami, Mikawa, Tōtōmi and Mutsu. According to some theories, the Miyoshi clan and the Mizukami clan were descendants of the Ogasawara clan.

The clan developed a number of schools of martial arts during this period, known as Ogasawara-ryū, and contributed to the codification of bushido etiquette.

Towards the end of the Sengoku period (late 16th century), the clan opposed both Toyotomi Hideyoshi and Tokugawa Ieyasu.

During the Edo period, the Ogasawara were identified as one of the fudai or insider daimyō clans which were hereditary vassals or allies of the Tokugawa, in contrast with the tozama or outsider clans.

The fudai Ogasawara clan originated in 12th century Shinano Province. They claim descent from Takeda Yoshikiyo and the Seiwa-Genji. Broadly, there are two genealogical lines of the Ogasawara, the Matsuo and the Fukashi, each of which identify places in Shinano. The Matsuo line gave rise to the Ogasawara of Echizen, and the Fukashi line is ultimately established at the Ogasawara of Bunzen.

The great-grandson of Yoshikiyo, Nagakiyo, was the first to take the name Ogasawara. The area controlled by his descendants grew to encompass the entire province of Shinano.

Nagakiyo's descendant, Ogasawara Hidemasa [ja] (1569–1615), served Ieyasu; and in 1590, Hidemasa received Koga Domain (20,000 koku) in Shimōsa Province. In 1601, Ieyasu transferred Hidemasa to Iida Domain (50,000 koku) in Shinano; then, in 1613, he was able to return to the home of his forebears, Fukashi Castle (80,000 koku), now known as Matsumoto Castle.