Iguaçu Falls, Salto Tres Mosqueteros (front), Salto Rivadavia (back, left), Salto Escondido (back, right)

Iguaçu Falls, Iguazu Falls, Iguazú Falls, or Iguassu Falls are waterfalls of the Iguazu River on the border of the Argentina province of Misiones and the Brazilian state of Paraná. The falls divide the river into the upper and lower Iguazu. For most of its course, the river flows through Brazil, however, most of the falls are on the Argentine side.

The name "Iguazu" comes from the Guarani or Tupi words "y", meaning "water", and "ûasú", meaning "big". Legend has it that a deity planned to marry a beautiful woman named Naipí, who fled with her mortal lover Tarobá in a canoe. In a rage, the deity sliced the river, creating the waterfalls and condemning the lovers to an eternal fall. The first European to record the existence of the falls was the Spanish conquistador Álvar Núñez Cabeza de Vaca in 1541.

Iguazu Falls is located where the Iguazu River tumbles over the edge of the Paraná Plateau, 23 kilometres upriver from the Iguazu's confluence with the Paraná River. Numerous islands along the 2.7-kilometre-long edge divide the falls into many separate waterfalls and cataracts, varying between 60 to 82 metres high. The number of these smaller waterfalls fluctuates from 150 to 300, depending on the water level. Approximately half of the river's flow falls into a long and narrow chasm called the Devil's Throat (Garganta del Diablo in Spanish or Garganta do Diabo in Portuguese). The Devil's Throat is U-shaped, 82 metres high, 150 m wide, and 700 m long. Placenames have been given also to many other smaller falls, such as San Martín Falls, Bossetti Falls, and many others.

About 900 metres of the 2.7-kilometre length does not have water flowing over it. The edge of the basalt cap recedes by 3 mm per year. The water of the lower Iguazu collects in a canyon that drains into the Paraná River, a short distance downstream from the Itaipu Dam.