The Musashino Line is a railway line operated by the East Japan Railway Company. It links Tsurumi Station in Yokohama with Nishi-Funabashi Station in Chiba Prefecture, forming a 100.6 km (62.5 mi) unclosed loop around central Tokyo. Passenger operations are limited to the 71.8 km (44.6 mi) portion between Fuchūhommachi and Nishi-Funabashi; the Tsurumi to Fuchūhommachi portion, called the "Musashino South Line", is normally used only by freight trains. The line forms part of what JR East refers to as the "Tokyo Mega Loop" around Tokyo, consisting of the Keiyō Line, Musashino Line, Nambu Line, and Yokohama Line.

The East Japan Railway Company is a major passenger railway company in Japan, the largest of the seven Japan Railways Group companies. The company name is officially abbreviated as JR-EAST or JR East in English, and as JR Higashi-Nihon in Japanese. The company's headquarters are in Yoyogi, Shibuya, Tokyo, next to Shinjuku Station. It is listed in the Tokyo Stock Exchange, is a constituent of the TOPIX Large70 index, and is one of three Japan Railways Group constituents of the Nikkei 225 index, the others being JR Central and JR West.