The Adirondack is a daily intercity passenger train operated by Amtrak between New York City and Montreal.

The scenic route follows the Empire Corridor through the Hudson Valley with major stops in Yonkers, Poughkeepsie, Albany–Rensselaer, and Schenectady.

North of Saratoga Springs the route runs between the Adirondack Mountains and Lake Champlain until crossing the Canada–U.S.

[6] The Adirondack began running on August 6, 1974 (with a ceremonial train the previous day) from Grand Central Terminal in New York to Albany, then over the D&H's line to Windsor Station in Montreal.

[13] In New York City, the opening of the Empire Connection on April 8, 1991, allowed the Adirondack to serve Penn Station instead of Grand Central.

Starting in 2012, Amtrak effectively took operational control of the Hudson Subdivision, handling all maintenance and capital responsibilities.

Presently, the Adirondack must stop at Lacolle, Quebec northbound and Rouses Point, New York southbound for immigration procedures that can take up to two hours.

[21] In March 2020, the Adirondack was truncated to Albany–Rensselaer after all non-essential travel across the Canada–United States border was banned in response to the COVID-19 pandemic.

During the COVID-19 suspension track conditions "deteriorat[ed]", forcing Amtrak to lengthen an already long running time between Rouses Point and Montreal.

[36] The Adirondack and Maple Leaf were combined between New York and Albany–Rensselaer beginning November 10, 2024, due to construction work in the East River Tunnels limiting capacity at Penn Station.

Unlike other Empire Corridor trains, the Adirondack does not offer business class seating.

[39] All cars offer complimentary WiFi, an electric outlet (120 V, 60 Hz AC) at each seat, reading lamps, and fold-out tray tables.

[41] Between New York City and Albany–Rensselaer, trains are pulled by a GE Genesis P32AC-DM dual-mode diesel locomotive at speeds up to 110 mph (177 km/h).