The Cross Island Line (CRL) is a high capacity Mass Rapid Transit (MRT) line under development in Singapore. It will run in an east–west direction from Changi to Jurong Industrial Estate via Loyang, Pasir Ris, Hougang, Serangoon North, Ang Mo Kio, Sin Ming, Bukit Timah, Clementi and West Coast. From Pasir Ris, the line will branch off to Punggol. The 58-kilometre (36 mi) line will replace the East West Line as the longest line on the MRT network upon its complete opening by the 2040s, serving about 27 stations.

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.