Rio de Janeiro–São Paulo megalopolis

The Rio de Janeiro–São Paulo Megalopolis, also known as the Brazilian Megalopolis is a megalopolis in Southern Brazil consisting of the cities of Rio de Janeiro and São Paulo, as well as their surrounding urban areas.

In 1999, Brian J. Godfrey wrote: "Even as Rio de Janeiro and Sao Paulo have sprawled to form the two main nuclei of an integrated megalopolis with a current population of between 30 and 60 million in southeastern Brazil, the two cities retain distinguishing characteristics."

In 2003, Jean Gottman, who studied the Northeast megalopolis in the 1960s, also suggested the formation of this megalopolis.

The entire Rio–São Paulo area is also sometimes considered a conurbation, and plans are in the works to connect the cities with a high-speed rail. Yet the government of Brazil does not consider this area a single unit for statistical purposes, and any population numbers would be synthetic. Another estimate published by Stanley D. Brunn, et al. suggests a population of 50 million.

As of December 2013, Rio de Janeiro to São Paulo is the third-busiest air traffic route by passenger volume, according to Amadeus.