The is a commuter and suburban electric multiple unit (EMU) train type developed by East Japan Railway Company (JR East) from the earlier E231 series and the E531 series design. The first train was introduced in December 2006 for use on the Chūō Line (Rapid), followed by the E233-1000 series variant in 2007 for use on the Keihin–Tōhoku and Negishi lines, the E233-3000 series outer-suburban variant in December 2007 for use on the Tōkaidō Main Line, and narrow-bodied E233-2000 series variant for Jōban Line and Tokyo Metro Chiyoda Line inter-running services. Further variants were built for use on the Keiyō Line, Yokohama Line, Saikyō Line, and Nambu Line.