The HEIDI dataset includes 2280 environments that were closed between the eighteenth century and the present (2017). All treaties share three definition criteria: (1) they are legally binding; (2) they have been completed by two or more States; 3) their main objective is to protect the natural world or to develop the sustainable exploitation of natural resources. These include well-known multilateral treaties on biodiversity and climate change, but the majority are bilateral or regional treaties on issues such as fisheries protection, freshwater management, oil pollution and nuclear waste. Most contracts were identified and collected by Ronald Mitchell (2003) . As treaties, HEAs are governed by international law and are binding after their entry into force. However, this does not always lead to compliance. National legislation is usually necessary to meet the standards of an environmental agreement. An agreement between two nations is called a bilateral environmental agreement. When the agreement is concluded between three or more nations, it is called a multilateral environmental agreement (MEA).
These agreements, concluded mainly by the United Nations, concern issues such as atmospheric policy, freshwater policy, waste and hazardous substances policy, the marine environment, nature protection policy, noise pollution and nuclear safety.  The full text of all IEL contracts is available in the International Environmental Database (IEA) project organized by the University of Oregon. This database includes more than 1300 multilateral environmental agreements (MEAS) and more than 2,200 bilateral environmental agreements (BEAs) and other agreements from the 1850s to the present day. It contains detailed pages for each agreement that contains links to the text, accession, performance data, secretariat and summary statistics. To take into account the specificities of each policy area, international scientists use the concept of «international regime, canonically defined as «a set of implicit or explicit principles, norms, rules and decision-making procedures that converge on the expectations of actors in a particular field of international relations» . . . .