Ecoregions are areas that:
 share a large majority of their species and ecological dynamics;
 share similar environmental conditions; and,
 interact ecologically in ways that are critical for their long-term persistence.
Scientists at the World Wildlife Fund (WWF), have established a classification system that divides the world in 867 terrestrial ecoregions, 426 freshwater ecoregions and 229 marine ecoregions that reflect the distribution of a broad range of fauna and flora across the entire planet.
The following is articles describe the terrestrial ecoregions of each country of the world. Many countries or regions commonly thought of as nations, but do not have generally recognized nation status (usually because they are being directly administered) by other nations are included, but not numbered.