The Korail Class 311000 trains, some train of which were formerly identified as Korail Class 5000 trains, are commuter electric multiple units in South Korea used on Seoul Subway Line 1. Class 311000 trains were manufactured and delivered between 1996 and 2006, and again from 2012 to 2014 to expand service on the Gyeongbu Line and the Gyeongwon Line, and to replace older trains.

Seoul Subway Line 1 of the Seoul Metropolitan Subway is a rapid transit and commuter rail line which links central Seoul, South Korea to Yeoncheon in the northeast, Incheon in the southwest, and Sinchang via Suwon and Cheonan in the south. The central underground portion of Line 1, running underneath Sejongno, Jongno, and Wangsan-ro avenues along Seoul's traditional downtown area, is the oldest subway-operated section in the Seoul Metropolitan Subway system. Its branches and services cover a large part of the Seoul Capital Area; totaling 218.3 km (135.6 mi) in route length.