This article provides the first explanation of the relationship between the three overlapping sources of national park law. It first explains how the Organic Act affords the National Park Service substantial discretion to manage the national parks, including deciding the proper balance between enjoyment and conservation in particular instances. It next shows how federal environmental statutes push national park management toward preservation rather than enjoyment. Third, Congress often intervenes to mandate particular management outcomes at individual parks, typically but not always toward enjoyment rather than preservation. The result is that the NPS has substantial discretion to manage national parks in a manner that pursues the dual Organic Act purposes of enjoyment and conservation, but Congress occasionally exercises its ultimate authority to specify which purpose should prevail in particular circumstances.