The Manila Metro Rail Transit System (MRTS), commonly known as the MRT, is a rapid transit system that primarily serves Metro Manila, Philippines. Along with the Manila Light Rail Transit System and the Metro Commuter Line of the Philippine National Railways, the system makes up Metro Manila's rail infrastructure.

Rapid transit or mass rapid transit (MRT), also known as metro, is a type of high-capacity public transport that is generally built in urban areas. A rapid transit system that primarily or traditionally runs below the surface may be called a subway, tube, or underground. Unlike buses or trams, rapid transit systems are railways, usually electric, that operate on an exclusive right-of-way, which cannot be accessed by pedestrians or other vehicles. They are often grade-separated in tunnels or on elevated railways.