Not all historians agree, but the origin and name "favela" comes from a plant, faveleira or mandioca-brava (Cnidoscolus phyllacanthus), a rough leguminous plant with leaves that cause urticaria and edible seeds, which grows on the hills or morros. In the past, when cariocas climbed the hills (cerros) to pick fruit and vegetables, they said that had come from the favelas, and so the name caught on for those housing settlements.

Although the first humble homes located in the hills of the city date back to 1865 and the first abolitionist law in Brazil, thousands of slaves were brought to Brazil by the Portuguese Empire (more than anywhere else) and this gave rise to a strong African culture throughout the country. The Law of Free Birth, which was passed on 28 September 1871 by the cabinet of the Viscount of Rio Branco, granted freedom to the children of slaves born after that date, although they remained under the supervision of their owners until they turned 21 years old. Finally, on 13 May 1888, the Imperial Government, through Princess Isabel, signed the so-called Golden Law that abolished slavery in Brazil. Many of these people had nowhere to go and settled in the hills.  

But as settlements, they have their origins at the start of the century when, in November 1897, 20,000 soldiers from Brazil's northeastern region, who had fought and won the War of Canudos in Bahia, arrived in the port of Rio de Janeiro. The government had promised them homes, but the red tape was endless, so after a while the soldiers stopped receiving salaries and grew tired of waiting, and they took the hill nearest Gamboa and began to build their houses in a very rudimentary way: crushed earth, pieces of wood, brick and scrapped metal sheets. The name soon became generic for slums around Rio and, by extension, those of many other large Brazilian cities like São Paulo.

Throughout the 20th century these settlements grew because of the economic contrast and poor distribution of space, migration and overpopulation (in the 40s there was a disproportionate increase in the population). None of these problems were ever solved by the different governments of Rio. 

The most economically disadvantaged people were building their houses with no urban planning, and the municipal government was not concerned with providing essential services to the slopes of the hills, and in the meantime Rio was becoming the most visited paradise on the planet.

Over the years the growth of the favelas created an environment conducive to crime, and drug trafficking organisations found that they provided the perfect place for refuge.

There are an estimated 968 favelas in Rio, inhabited by some two million people.

They are testimony to the unequal distribution of wealth in the country, since 34% of Brazil's population lives below the poverty line. These chaotic favelas have been out of control for decades. In the past it was too dangerous to enter them, even for Brazilians themselves.

However, thanks to a positive and gradual change in attitude that began in the mid-90s, efforts to reintegrate the favelas into the city are paying off.

In recent years, the bad image of favelas has softened somewhat, and they have managed to spread their fame in a positive way thanks to painting, music and sports.

Despite their historic infamy, Rio's favelas are part of the cultural wealth of the city, as much as Christ the Redeemer, the Maracanã Stadium and Carnival.

Immersed in a process of change, especially due to the Brazil's election as the host country for two very important international events, the World Cup and the Olympics, the government has found the motivation it lacked to remedy the most urgent problems of the favelas.

The biggest change has occurred with the introduction of UPPs (Pacifying Police Units), which are controlling more areas and have managed to make a dozen favelas safer. The introduction of these police forces benefits both visitors, who want to find out about favelas, and those who live there.