Keio Corporation (Japanese: 京王電鉄株式会社, Hepburn: Keiō Dentetsu Kabushiki-gaisha, 'Keio Electric Railway K.K') is a private railway operator in Tokyo, Japan and the central firm of the Keio Group (京王グループ, Keiō Gurūpu) that is involved in transport, retail, real estate and other industries.

[4] The Inokashira Line began operating in 1933 as a completely separate company, Teito Electric Railway (帝都電鉄).

[4] In 1947, the shareholders of Tokyu voted to spin off the Keio and Inokashira lines into a new company, Keiō Teito Electric Railway (京王帝都電鉄).

[4] The Teito name was dropped in 1998 in favor of Keio Electric Railway (京王電鉄, Keiō Dentetsu), though "KTR" placards and insignia can still be seen occasionally.

The first of a fleet of five new ten-car 5000 series EMUs was introduced on 29 September 2017, ahead of the start of new evening reserved-seat commuter services from Shinjuku in spring 2018.