The Saikyō Line (Japanese: 埼京線, romanized: Saikyō-sen) is a Japanese railway line operated by the East Japan Railway Company (JR East). 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 (Japanese: 埼玉) and Tōkyō (Japanese: 東京).
At the northern end of the line, some trains continue beyond Ōmiya as far as Kawagoe on the Kawagoe Line; at the southern end of the line, many Saikyō Line trains continue onward beyond Ōsaki to either Shin-Kiba on the Rinkai Line (operated by Tokyo Waterfront Area Rapid Transit) or Ebina on the Sotetsu Main Line (via the Sōtetsu Shin-Yokohama Line). Moreover, despite the line’s name, some trains only go between Kanagawa and Shinjuku, without continuing to Saitama. Beside the link that connects the Saikyō and Rinkai lines is the JR East Tokyo General Rolling Stock Centre that stores the rolling stock for the Yamanote Line and other types of rolling stock; and the Hinkaku Line which links Saikyo Line to the Tokaido Freight Line and Sotetsu-JR Link Line.