The Niagara Escarpment is an approximately 1,050-kilometre-long (650-mile) discontinuous, arc-shaped, but generally northward-facing escarpment, or cuesta, in Canada and the United States. The escarpment begins south of Lake Ontario and circumscribes the top of the Great Lakes Basin running from New York through Ontario, Michigan, and Wisconsin. The escarpment is the cliff over which the Niagara River plunges at Niagara Falls, for which it is named.

The escarpment is a UNESCO World Biosphere Reserve. The reserve has the oldest forest ecosystem and trees in eastern North America.

The Niagara Escarpment is not a fault line but the result of unequal erosion. The cliff-forming rock exposed along the escarpment is a belt of limestone and dolomite of the Lockport Formation of Silurian age. The Niagara Escarpment is the most prominent of several escarpments formed in the bedrock of the Great Lakes Basin. For example, the Onondaga Formation, which runs in a parallel outcrop belt just to the south of the Lockport Formation through western New York and southern Ontario, forms a separate escarpment. The Niagara Escarpment traces, and in part shapes, the individual basins and landforms of Lake Ontario, Lake Huron, and Lake Michigan.

In Rochester, New York, the Genesee River flows through the city in three waterfalls over the scarp face. The escarpment thence runs westward to the Niagara River, forming a deep gorge north of Niagara Falls, which itself cascades over the scarp face. In Southern Ontario, it spans the Niagara Peninsula, closely following the Lake Ontario shore through the cities of St. Catharines and Hamilton, where it takes a sharp turn north in the town of Milton toward Georgian Bay. It then follows the Georgian Bay shore northwestwards to form the spine of the Bruce Peninsula and Manitoulin Island, as well as several smaller islands in northern Lake Huron, where it turns westwards into the Upper Peninsula of northern Michigan, south of Sault Ste. Marie. It extends down the Garden Peninsula and Potawatomi Islands into Wisconsin following the Door Peninsula and then continues more inland from the western coast of Lake Michigan until ending in the southeastern corner of Dodge County north of Chicago, Illinois.

Study of rock exposures and drillholes demonstrates that no displacement of the rock layers occurs at the escarpment, which is not a fault line but the result of unequal erosion. The escarpment's caprock is dolomitic limestone, also known as dolostone, which is more resistant and overlies weaker, more easily eroded shale as a weathering-resistant "cap". The escarpment formed over millions of years through a process of differential erosion of these rocks of different hardnesses. Through time the soft rocks weather away or erode by the action of streams. The gradual removal of the soft rocks undercuts the resistant caprock, leaving a cliff or escarpment. The erosional process is most readily seen at Niagara Falls, where the river has quickened the process. It can also be seen at the three waterfalls of the Genesee River at Rochester (additional resistant rock layers make more than one escarpment in some places). Also, in some places thick glacial deposits, such as the Oak Ridges Moraine, conceal the Niagara Escarpment, such as north of Georgetown, Ontario, where it actually continues under glacial till and reappears farther north.^{[citation needed]}

The dolomite cap was laid down as sediment on the floor of a marine environment. In Michigan, behind (south of) the escarpment, the cuesta capstone slopes gently to form a wide basin, the floor of an Ordovician-Silurian-age tropical sea. (The escarpment is essentially the remnant shoreline of that sea.) There the constant deposition of minute shells and fragments of biologically generated calcium carbonate, mixed with sediment washed in by erosion of the virtually lifeless landmasses, eventually formed a limestone layer. During the Silurian period, some magnesium substituted for some of the calcium in the carbonates, slowly forming harder dolomite layers in the same fashion. This dolomite basin contains Lakes Michigan, Huron, and Erie. Worldwide sea levels were at their all-time maximum in the Ordovician; as the sea retreated, erosion inevitably began.

The escarpment was a major obstacle in the construction of the Erie Canal in New York and was traversed by a series of locks; the community which grew up at the site thus became known as Lockport, New York.

The Welland Canal allows ships to traverse the escarpment between Lake Erie and Lake Ontario on the Niagara Peninsula of Ontario. The canal also allowed Sea Lamprey, an invasive species native to Northern Atlantic Ocean, to enter Lake Erie and became a concern for the lake's ecosystem.