The Staten Island Railway (SIR) is a rapid transit line in the New York City borough of Staten Island. It is owned by the Staten Island Rapid Transit Operating Authority (SIRTOA), a subsidiary of the Metropolitan Transportation Authority, and operated by the New York City Transit Authority Department of Subways. SIR operates 24 hours a day, seven days a week, providing local service between St. George and Tottenville, along the east side of the island. The only line on the island, there is no direct rail link between the SIR and the New York City Subway system, but SIR riders do receive a free transfer to New York City Transit bus and subway lines, and the line is included on official New York City Subway maps. Commuters on the railway typically use the Staten Island Ferry to reach Manhattan; the line is accessible from within the Ferry Terminal, and most of its trains connect with the ferry.

The line has a route bullet similar to other subway routes: the letters SIR in a blue circle. It is used on timetables, the MTA website, and some signage, but not on trains. Like the New York City Subway, the line runs 24 hours a day every day of the year, and is one of the few 24/7 mass-transit rail systems in the United States.

Although the railway was originally considered a standard rail line, the existing line is severed from the national rail system, and only a small portion of the former North Shore Branch still sees freight use. The passenger operations are now regulated as a rapid transit system, and exempt from certain regulations. The line uses modified R44 subway cars, with planned replacement by R211 cars.