Line 2 of the Beijing Subway is a rapid transit rail line in central Beijing that runs in a rectangular loop around the city centre. The line traces the Ming dynasty inner city wall, which was demolished and paved over by the 2nd Ring Road and Qianmen Avenue to make room. Line 2, opened in 1984, is the second oldest and one of the busiest of Beijing's subway lines, and to date only one to serve Beijing railway station. All 18 stations on the 23.1 km (14.4 mi) line are underground. 12 of the 18 stations offer transfers to other lines, with the number growing to 13 with the opening of Line 3 in late 2024. Line 2's color is dark blue.

The Beijing Subway is the rapid transit system of Beijing Municipality that consists of 27 lines including 22 rapid transit lines, two airport rail links, one maglev line and 2 light rail lines, and 490 stations. The rail network extends 836 km (519 mi) across 12 urban and suburban districts of Beijing and into one district of Langfang in neighboring Hebei province. With 3.8484 billion trips delivered in 2018, an average of 10.544 million trips per day, the Beijing Subway is the world's busiest metro system. Single-day ridership set a record of 13.7538 million on July 12, 2019. Being 836 kilometres (519 mi) in system length, the Beijing Subway is the longest metro system by route length, surpassing the Shanghai Metro in December 2023.