The 23rd Street Crosstown is a surface transit line on 23rd Street in Manhattan, New York City. It currently hosts the M23 SBS bus route of the Metropolitan Transportation Authority (MTA)'s Regional Bus Operations. The M23 runs between Chelsea Piers, along the West Side Highway near 22nd Street, via 23rd Street, to Avenue C and 20th Street in Stuyvesant Town–Peter Cooper Village.
The route was originally the Twenty-third Street Railway, a street railway that was originally operated as horse cars and later electric traction. The company was chartered on January 29, 1872. The Twenty-third Street Railway was leased by numerous larger companies in the late 19th and early 20th century. The trolley line was replaced with bus service in 1936 and was originally numbered the M18-15 and the M26 before gaining the current M23 designation in 1989. On November 6, 2016, it became a Select Bus Service (SBS) route.