The Ōu Main Line is a railway line in Japan, operated by the East Japan Railway Company. It connects Fukushima Station through Akita Station to Aomori Station. Since the opening of the Yamagata Shinkansen on July 1, 1992, the Fukushima–Yamagata section is sometimes referred to as the Yamagata Line. The name of the line as a whole refers to the ancient provinces of Mutsu (陸奥) and Dewa (出羽), as it connects both ends of Mutsu by passing north–south through Dewa.

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.