The namesake and unifying feature of the Northern Appalachian–Acadian (NAP) Ecoregion are the northern Appalachian Mountains, which, along with maritime and coast influences, have defined the geologic, natural and cultural history of the northeast.
The NAP Ecoregion extends from the Tug Hill and Adirondack ranges of New York, across the Green Mountains of Vermont and the White Mountains of New Hampshire, then into Maine and Maritime Canada. It includes all the provinces of New Brunswick, Nova Scotia, and Prince Edward Island, as well as Îles-de-la-Madeleine (Magdalene Islands) and the part of Québec extending from the Gaspé Peninsula, southwesterly through the Appalachian complex of eastern Québec to the United States border, south of Sherbrooke.