Musashi (武蔵国; -no kuni) was a province of Japan, which today composes Tokyo prefecture, most of Saitama Prefecture and part of Kanagawa Prefecture, mainly Kawasaki and Yokohama. Musashi bordered on Kai, Kōzuke, Sagami, Shimōsa, and Shimotsuke Provinces.

Musashi was the largest province in the Kanto region. It had its ancient capital in modern Fuchu, Tokyo and its provincial temple in what is now Kokubunji, Tokyo. By the Sengoku period, the main city was Yedo, which became the dominant city of eastern Japan. Edo Castle was the headquarters of Tokugawa Ieyasu before the Battle of Sekigahara and became the dominant city of Japan during the Edo period, being renamed Tokyo during the Meiji restoration.

It gave its name to the battleship of the Second World War Musashi.