There exist different classifications of treaties. Political treaties include alliances, peace settlements, disarmament agreements, and territorial settlements. Commercial treaties deal with tariffs, fishing rights, navigation, and the opening of consulates and offices of tourism. Some treaties are constitutional or administrative documents. The United Nations Charter is an example. Such treaties establish and regulate international organizations and specialized agencies. There are treaties that deal with criminal justice, that define international crimes such as terrorism, and that provide for extradition, or the process by which one state surrenders to another an individual for trial. Treaties pertaining to civil law are conventions for the protection of human rights and for the enforcement of trade mark and copyright laws. The codifying of international law also comes within the scope of treaties. These include rules for the conduct of war and the settlement of disputes. A single treaty often embraces several of these elements.
The principle that treaties must be observed – pacta sunt servanda– constitutes the foundation of the law of treaties. The Vienna Convention on the Law of Treaties states this as follows: “Every treaty in force is binding upon the parties to it and must be performed by them in good faith.” This means that each treaty that is legitimately in force is legally binding on all signatories. It must be carried out in good faith, i.e. not formally but honestly; each signatory State has the duty to take all measures necessary to carry out the treaty's provisions in accordance with its aims and principles. The principle of good faith prohibits abuses of treaty rights – that is, their use to the disadvantage of the legitimate rights and interests of other States. Finally, an important substantive element of the principle that “treaties must be observed” is that a State may refuse to implement a treaty or limit its implementation only on the basis of international law. A signatory State does not have the right to refer to its own domestic law to justify the non-execution of treaties.