An ecozone or biogeographic realm is the largest scale biogeographic division of the earth's surface.

These divisions are based on the historic and evolutionary distribution of plants and animals. Ecozones represent large areas of the Earth surface where plants and animals developed in relative isolation over long periods of time, and are separated from one another by geologic features, such as oceans, broad deserts, or high mountain ranges, that formed barriers to plant and animal migration. Ecozones correspond to the floristic kingdoms of botany or zoogeographic regions of mammal zoology.