Constitutional provisions are extraordinarily strong mechanisms for reaching legal ends, e.g. environmental protection, for a number of reasons. Constitutional provisions are “entrenched” within legal systems. The spectrum of constitutional environmental rights is generally broad and varied. In many countries, there may be no mention of environmental protection in the constitution, but it may be effectively treated as if it were—often through the protection of human rights. Some cultures have introduced references to the right to a favorable environment in their catalogues of constitutional rights. The ecocentric tradition of constitutional environmental rights has provided the rights of nature with a form of legal personhood. Subnational constitutions are foundational documents which may be identical to, similar to, or substantially different than their national counterparts. Constitutional organization of the twenty-first century sovereign state spans a spectrum from exceptional unitarianism to a complete dual federal–state system.