The Amazon River (UK: , US: ; Spanish: Río Amazonas, Portuguese: Rio Amazonas) in South America is the largest river by discharge volume of water in the world, and the disputed longest river system in the world in comparison to the Nile.

The headwaters of the Apurímac River on Nevado Mismi had been considered for nearly a century the Amazon basin's most distant source until a 2014 study found it to be the headwaters of the Mantaro River on the Cordillera Rumi Cruz in Peru. The Mantaro and Apurímac rivers join, and with other tributaries form the Ucayali River, which in turn meets the Marañón River upstream of Iquitos, Peru, forming what countries other than Brazil consider to be the main stem of the Amazon. Brazilians call this section the Solimões River above its confluence with the Rio Negro forming what Brazilians call the Amazon at the Meeting of Waters (Portuguese: Encontro das Águas) at Manaus, the largest city on the river.

The Amazon River has an average discharge of about 215,000 m³/s (7,600,000 cu ft/s)–230,000 m³/s (8,100,000 cu ft/s)—approximately 6,591 km³ (1,581 cu mi)– 7,570 km³ (1,820 cu mi) per year, greater than the next seven largest independent rivers combined. Two of the top ten rivers by discharge are tributaries of the Amazon river. The Amazon represents 20% of the global riverine discharge into oceans. The Amazon basin is the largest drainage basin in the world, with an area of approximately 7,000,000 km² (2,700,000 sq mi). The portion of the river's drainage basin in Brazil alone is larger than any other river's basin. The Amazon enters Brazil with only one-fifth of the flow it finally discharges into the Atlantic Ocean, yet already has a greater flow at this point than the discharge of any other river.