Western New York is the westernmost region of the state of New York. It includes the cities of Buffalo, Rochester, Niagara Falls, Jamestown and the surrounding suburbs, as well as the outlying rural areas of the Great Lakes lowlands, the Genesee Valley, and the Southern Tier. The historic beginnings of the region can be defined by its original eastern boundary of Preemption Line, created by the December 16, 1786 political settlement between the states of New York and Massachusetts, both of which claimed political dominion over the land. This eastern boundary shifted because of changing county borders in the late 18th and early 19th centuries.

Western New York consists of 17 western counties in New York State: Allegany, Cattaraugus, Chautauqua, Chemung, Erie, Genesee, Livingston, Monroe, Niagara, Ontario, Orleans, Schuyler, Seneca, Steuben, Wayne, Wyoming, and Yates, with a land area of 11,764 square miles (30,470 km2). Western New York includes the area of the Holland Purchase and the Phelps and Gorham Purchase. The area is primarily served by Buffalo and Rochester media markets, although there is considerable overlap between these two markets, as well as other American and Canadian media markets (particularly from nearby Toronto). In terms of the combined statistical areas used by the United States Census Bureau, Western New York consists of the Buffalo-Cheektowaga-Olean, NY area, the Rochester-Batavia-Seneca Falls, NY area, and the Elmira-Corning, NY area.

Western New York is in some contexts considered a sub-region of “Upstate New York” (when that term is used to describe all of New York State outside Long Island and the New York City metropolitan area); in other contexts it is considered a separate region from “Upstate.” While the term usually includes both the Buffalo and Rochester metropolitan areas, occasionally “Western New York” describes only the Buffalo-Niagara region, with Greater Rochester being classified as part of the Finger Lakes Region.