The Circle Line (CCL) is a medium-capacity Mass Rapid Transit line in Singapore. It runs in a loop from Dhoby Ghaut station in the city-centre to HarbourFront station in the south via Bishan station in the centre of the country. It also has a branch to Marina Bay station from Promenade station, which will be extended to HarbourFront station from 2026 to form a complete loop. Coloured orange on the rail map, the fully-underground line is approximately 35.5 kilometres (22.1 mi) long with 30 stations. Travelling from one end of the line to the other takes about an hour.

The Mass Rapid Transit system, locally known by the initialism MRT, is a rapid transit system in Singapore and the island country's principal mode of railway transportation. The system commenced operations in November 1987 after two decades of planning with an initial 6 km (3.7 mi) stretch consisting of five stations. The network has since grown to span the length and breadth of the country's main island – with the exception of the forested core and the rural northwestern region – in accordance with Singapore's aim of developing a comprehensive rail network as the backbone of the country's public transportation system, averaging a daily ridership of 3.4 million in 2019.