Tropical rainforests are a world like none other; and their importance to the global ecosystem and human existence is paramount. Unparalleled in terms of their biological diversity, tropical rainforests are a natural reservoir of genetic diversity which offers a rich source of medicinal plants, high-yield foods, and a myriad of other useful forest products. They are an important habitat for migratory animals and sustain as much as 50 percent of the species on Earth, as well as a number of diverse and unique indigenous cultures. Tropical rainforests play an elemental role in regulating global weather in addition to maintaining regular rainfall, while buffering against floods, droughts, and erosion. They store vast quantities of carbon, while producing a significant amount of the world's oxygen.  
 
 Despite their monumental role, tropical forests are restricted to the small land area between the latitudes 22.5° North and 22.5° South of the equator, or in other words between the Tropic of Capricorn and the Tropic of Cancer. Since the majority of Earth's land is located north of the tropics, rainforests are naturally limited to a relatively small area.  
  
Tropical rainforests, like so many other natural places, are a scarce resource in the 21st century. The vast swaths of forest, swamp, desert, and savanna that carpeted Earth's land surface a mere five generations ago have been reduced to scattered fragments; today, more than two-thirds of the world's tropical rainforests exist as fragmented remnants. Just a few thousand years ago, tropical rainforests covered as much as 12 percent of the Earth’s land surface, or about 6 million square miles (15.5 million square km), but today less than 5 percent of Earth's land is covered with these forests (about 2.41 million square miles or 625 million hectares). The largest unbroken stretch of rainforest is found in the Amazon river basin of South America. Over half of this forest lies in Brazil, which holds about one-third of the world's remaining tropical rainforests. Another 20 percent of the world's remaining rainforest exists in Indonesia and Congo Basin, while the balance of the world's rainforests are scattered around the globe in tropical regions.  
 
The global distribution of tropical rainforests can be broken up into four biogeographical realms based roughly on four forested continental regions: the Ethiopian or Afrotropical, the Australiasian or Australian, the Oriental or Indomalayan/Asian, and the Neotropical.

Rainforest cover by biogeographically realm