The type evolved from the earlier 209 series and E217 series EMUs, and the prototype train built in 1998 for trials on the Chūō–Sōbu Line was actually classified 209-950 series, later becoming E231-900 series. Full-production E231-0 series trains were subsequently introduced on the Chūō–Sōbu Line (10-car sets) and Jōban Line (10+5-car sets). Other variants include the 11-car E231-500 series for the Yamanote Line, and the E231-800 series with 2,800 mm (9 ft 2 in) wide bodies and end doors for use on Tokyo Metro Tozai Line inter-running services.
