The Saikyō Line is a Japanese railway line operated by the East Japan Railway Company. It connects Ōsaki Station in Shinagawa, Tokyo, and Ōmiya Station in Saitama Prefecture. The line's name is a portmanteau of the two areas the line connects: Saitama and Tōkyō.

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.