The “energy sector” is generally interpreted as referring to industries focused on the (•) extraction, (•) refining, (•) transport, (•) use of various forms of energy, and (•) related research and associated infrastructure. Despite the fact that no law or regulation contains any general definition of the energy sector, the Energy Charter Treaty contains at least the fundamental guidelines and identification of terms. The ECT provides a multilateral framework for energy cooperation that is unique under international law. In its Preamble, the ECT refers to the Charter of Paris for a New Europe as a declaration of the new era of peaceful cooperation of countries following the end of the Cold War. The ECT thereby creates a binding legal basis for permanent economic cooperation in the energy sector. It is the first multilateral treaty for the protection of investments, i.e. a binding source of international law. The Charter and the ensuing ECT are not the only multilateral initiatives in the energy sector; however, it is the only multilateral treaty providing a substantive-law international basis from the perspective of energy investments protection. Other important general treaties and conventions in the energy sector include the Convention on Long-Range Transboundary Air Pollution, the Charter of Paris for a New Europe – OSCE, and the United Nations Framework Convention on Climate Change.