Land law is the form of law that deals with the rights to use, alienate, or exclude others from land. In many jurisdictions, these kinds of property are referred to as real estate or real property, as distinct from personal property. Land use agreements, including renting, are an important intersection of property and contract law. Encumbrance on the land rights of one, such as an easement, may constitute the land rights of another. Mineral rights and water rights are closely linked, and often interrelated concepts. Land rights are such a basic form of law that they develop even where there is no state to enforce them; for example, the claim clubs of the American West were institutions that arose organically to enforce the system of rules appurtenant to mining. Squatting, the occupation of land without ownership, is a globally ubiquitous phenomenon.