The Seibu 30000 series (西武30000系) is an electric multiple unit (EMU) train type operated by the private railway operator Seibu Railway on commuter services in the Tokyo area of Japan. First introduced in April 2008, a total of six 10-car sets, eighteen 8-car sets, and six 2-car sets were built by Hitachi Rail between 2008 and 2016 to replace older three-door 101 series and 301 series sets. It is nicknamed the "Smile Train" .

Seibu Railway Company, Ltd. is a conglomerate based in Tokorozawa, Saitama, Japan, with principal business areas in railways, tourism, and real estate. Seibu Railway's operations are concentrated in northwest Tokyo and Saitama Prefecture; the name "Seibu" is an abbreviation of "west Musashi", referring to the historic name for this area. It and its holding company hold shares of numerous bus, hotel and tourism operations nationwide.