The Minatomirai 21 Line, commonly known as the Minatomirai Line, is a subway line in Yokohama, Japan that runs from Yokohama Station to Motomachi-Chūkagai Station through the Minatomirai 21 business district. The line opened in 2004 and is operated by the Yokohama Minatomirai Railway Company.

Yokohama is the second-largest city in Japan by population and by area, and the country's most populous municipality. It is the capital and most populous city in Kanagawa Prefecture, with a population of 3.7 million in 2023. It lies on Tokyo Bay, south of Tokyo, in the Kantō region of the main island of Honshu. Yokohama is also the major economic, cultural, and commercial hub of the Greater Tokyo Area along the Keihin Industrial Zone.