The Metro North West Line is a rapid transit rail line in Sydney, New South Wales, Australia. The first and currently the only line on the Sydney Metro network, it commenced operation on 26 May 2019, running between Tallawong and Chatswood.

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.