The MRT Yellow Line is an elevated monorail line in Bangkok and Samut Prakan Province, Thailand, part of the MRT rapid transit system. The 30.4 km (18.9 mi) line has 23 stations and cost 55 billion baht. The line was originally proposed in 2005 by the Office of Transport and Traffic Policy and Planning to be a heavy rail underground line along Lat Phrao road which was then elevated from Lam Sali Intersection to Samrong. However, it was decided in 2012 to build an elevated monorail line for the whole length in order to reduce construction costs.

The Metropolitan Rapid Transit or MRT is a mass rapid transit system serving the Bangkok Metropolitan Region in Thailand. The MRT system comprises two fully operational rapid transit lines and one fully operational monorail line (Yellow). One monorail line (Pink) is in trial operation, with another rapid transit line (Orange) under construction. The MRT Blue Line, officially the Chaloem Ratchamongkhon Line, between Hua Lamphong and Bang Sue was the first to open in July 2004 as Bangkok's second metro system. The MRT Blue line is officially known in Thai as rotfaifa mahanakhon (รถไฟฟ้ามหานคร) or "metropolitan electric train", but it is more commonly called rotfai taidin (รถไฟใต้ดิน), literally, "underground train" as it was distinguished from the BTS Skytrain by being completely underground when its first section between Hua Lamphong to Bang Sue opened.