The megadiverse countries are a group of countries that harbor the majority of the Earth's species and are therefore considered extremely biodiverse. Conservation International identified 17 megadiverse countries in 1998. All are located in, or partially in, the tropics.

In 2002, Mexico formed a separate organization focusing on Like-Minded Megadiverse Countries, consisting of countries rich in biological diversity and associated traditional knowledge. This organization does not include all the megadiverse countries as identified by Conservation International.

In alphabetical order, the 17 countries are:

On 18 February 2002, the Ministers in charge of the Environment and the Delegates of Brazil, China, Colombia, Costa Rica, India, Indonesia, Kenya, Philippines, Mexico, Peru, South Africa and Venezuela assembled in the Mexican city of Cancún. These countries declared to set up a Group of Like-Minded Megadiverse Countries as a mechanism for consultation and cooperation so that their interests and priorities related to the preservation and sustainable use of biological diversity could be promoted. They also declared that they would call on those countries that had not become Parties to the Convention on Biological Diversity, the Cartagena Protocol on Biosafety, and the Kyoto Protocol on climate change to become parties to these agreements.