During the twentieth century, the focus of North American heritage conservation activity has shifted from the preservation of isolated landmarks to the protection of entire urban districts. In the United States, heritage conservation - in the form of historic district designations - has become an effective planning tool in the regulation and management of the urban environment. This has been made possible by a succession of federal laws combining the principles of heritage conservation with those of environmental protection, and by the development of federal-state co-operative funding and support programs. In Britain, conservation and environmental planning concerns complement one another through a series of integrated planning statutes.
In Canada, at both the federal and provincial levels, environmental planning and heritage conservation programs have been developed and administered separately. This is particularly evident in Ontario, where urban planning programs frequently operate at cross purposes to those of conservation. Lack of co-ordination between legislative acts and their administrative government ministries, and lack of funding, have jeopardized the success of many heritage conservation efforts.