A key component of Seoul's industrialization, as its population boomed, was to put in a subway system. Originally planned as a modest 5-line system around downtown (of which only one line was completed, in 1974), a revised 4-line system extending to most parts of the city was completed by the mid-1980s, and four additional lines and suburban services added by the late 1990s. Today, Seoul's subway system is one of the greatest in the world, by both trackage and ridership; expansions of the system continue today.

This is Line 2, the busiest line. The first section opened in 1980, to connect eastern downtown to Jamsil and its Olympic facilities. By 1984, it became a full circle line with 43 stations, spurring development in the southern parts of the city. At 60 kilometers, it is the longest circular subway line in the world, with a running time of 86 minutes for a full circle. Seoul Metro, a city-owned public corporation, is responsible for operating Line 2.