Holarctic region, one of the six major land areas of the world defined on the basis of its characteristic animal life. It encompasses all the nontropical parts of Europe and Asia, Africa north of the Sahara, and North America south to the Mexican desert region. This vast region is often subdivided into the Palaearctic (Old World) and Nearctic (New World) subregions. The vegetational divisions roughly corresponding to this region are the Boreal and Palaeotropical (in part) kingdoms. The animals and plants of the region include a vast array of fishes, amphibians, reptiles, birds, and mammals.