In the United States there are the following principal categories of nature reserves: national parks, national forests, national wildlife refuges and Taylor Grazing Act districts.

In national parks nature is left to her own devices, unless interference is essential, to control, for example, a superabundance of grazing animals which are ravaging their food supply. Trees are not cut, nor dead ones removed. Roads and buildings are made as inconspicuous as possible. Wildlife refuges are managed for the benefit of the species for which they have been established, usually upland or water birds. National forests were originally established for watershed protection and timber supply.