Niagara Falls are a set of massive waterfalls located on the Niagara River in eastern North America, on the Canada–United States border between the Canadian province of Ontario and the U.S. state of New York. It comprises three waterfalls: Horseshoe Falls in Canada and American Falls and the smaller, adjacent Bridal Veil Falls in the United States. The falls are located 17 miles (27 km) from the city of Buffalo, New York, and 75 miles (120 km) from Toronto, Ontario.

Niagara Falls formed after glaciers receded at the end of the Wisconsin glaciation (the last ice age), as water from the newly-formed Great Lakes carved a path through the Niagara Escarpment en route to the Atlantic Ocean. While not exceptionally high, Niagara Falls is very wide; with more than six million cubic feet of water falling over the crestline every minute in high flow, and almost 4 million cubic feet on average, it is the most powerful waterfall in North America.

Niagara Falls is renowned both for its beauty and as a valuable source of hydroelectric power for Ontario and New York. Preserving this natural wonder from commercial over-development, while allowing for the needs of the area's people, has been a challenging project for environmentalists since the 1800s. A popular tourist site for over a century, the Falls are shared between the twin cities of Niagara Falls, Ontario and Niagara Falls, New York.