A rainforest is a dense evergreen forest occupying a tropical region with an annual rainfall of at least 2.5 meters.

These dense forests contain many fruits, animals, and insects. The rainforest contains trees with products that can be turned into rubber, tea, coffee, and sugarcane. Another thing they contain is cacoa beans.

Rain forests may be grouped into two major types: tropical and temperate. Tropical rain forest is characterized by broadleaf evergreen trees that form a closed canopy, below which is found a zone of vines and epiphytes (plants growing on the trees), a relatively open forest floor, and a very large number of species of both plant and animal life. The largest trees have curved trunks and emerge above the continuous canopy, while smaller trees commonly form a layer of more shade-tolerant species beneath the upper canopy. The maximum height of the upper canopy of tropical rain forests is generally about 30 to 50 m (100 to 165 ft), with some individual trees rising as high as 60 m (200 ft) above the forest floor.

The largest areas of tropical rain forest are in the Amazon basin of South America, in the Congo basin and other lowland equatorial regions of Africa, and on both the mainland and the islands off Southeast Asia, where they are especially abundant on Sumatra and New Guinea. Small areas are found in Central America and along the Queensland coast of Australia.

Temperate rain forests, growing in higher-latitude regions having wet, maritime climates, are less extensive than those of the tropics but include some of the most valuable timber in the world. Notable forests in this category are those on the northwest coast of North America, in southern Chile, in Tasmania, and in parts of southeastern Australia and New Zealand. These forests contain trees that may exceed in height those of tropical rain forests, but there is less diversity of species.

Rain forests cover less than six percent of the Earth's total land surface, but they are the home for up to three-fourths of all known species of plants and animals; they also contain many more species as yet undiscovered. Recent studies suggest that this great diversity of species is related to the apparently dynamic and unstable nature of rain forests over geologic time. Despite their appearance of fertile abundance, rain forests are fragile ecosystems. Their soils can quickly lose the ability to support most forms of vegetation once the forest cover is removed, and some soils even turn into hard laterite clay. The effect of forest removal on local climates is also often profound, although the role of rain forests in world climatic changes is not yet clear.

Throughout history, humans have destroyed rain forests for living space, timber, and agricultural purposes. In vast portions of upland tropical forests, the practice of "shifting cultivation" has caused deterioration of the primary forest. In this system of agriculture, trees are killed in small plots that are cropped for two or three seasons and then abandoned; if the plots are recultivated before primary vegetation has reestablished itself, a progressive deterioration of the forest results. Logging for exotic tropical wood has grown extensively in recent decades, leading to rapid deforestation of rain forests in places such as Brazil, Central America, and Malaysia. Temperate rain forests in British Columbia, Canada, are also in danger from logging.

Numerous organizations are now attempting to reduce the rate of the loss. As part of the response to deforestation, a number of tropical rain forest sanctuaries have been established around the world. Pharmaceutical companies have also taken an interest preserving tropical rain forests, which may have plants of medicinal value among their many plants.