Sources of international law

primary source of international lawSourcesa source of international lawgeneral principles of international lawgeneral principles of lawstate practice
International law also known as "law of nations" is the name of a body of rules which regulate the conduct of sovereign states in their relations with one another.wikipedia
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International law

public international lawinternationallaw of nations
International law also known as "law of nations" is the name of a body of rules which regulate the conduct of sovereign states in their relations with one another.
The sources of international law include international custom (general state practice accepted as law), treaties, and general principles of law recognized by most national legal systems.

Customary international law

customaryinternational customary lawcustom
Sources of international law include treaties, international customs, general principles of law as recognized by civilized nations, the decisions of national and lower courts, and scholarly writings. Derived from the consistent practice of (originally) Western states accompanied by opinio juris (the conviction of States that the consistent practice is required by a legal obligation), customary international law is differentiated from acts of comity (mutual recognition of government acts) by the presence of opinio juris (although in some instances, acts of comity have developed into customary international law, i.e. diplomatic immunity).
Along with general principles of law and treaties, custom is considered by the International Court of Justice, jurists, the United Nations, and its member states to be among the primary sources of international law.

Treaty

treatiesinternational treatyinternational treaties
Sources of international law include treaties, international customs, general principles of law as recognized by civilized nations, the decisions of national and lower courts, and scholarly writings. During the 19th century, it was recognized by legal positivists that a sovereign could limit its authority to act by consenting to an agreement according to the principle pacta sunt servanda. Pursuant to Chapter XVI, Article 103 of the United Nations Charter, the obligations under the United Nations Charter overrides the terms of any other treaty.
As one of the earliest manifestations of international relations, treaties are recognized as a primary source of international law.

Law

legallawslegal theory
They have been influenced by a range of political and legal theories.

International community

ICInternationalinternational communities
They are the materials and processes out of which the rules and principles regulating the international community are developed.

Sovereign state

statestatessovereign states
International law also known as "law of nations" is the name of a body of rules which regulate the conduct of sovereign states in their relations with one another.

Statute of the International Court of Justice

ICJ Statuteparties to the Statute of the International Court of Justice
Article 38 (1) of the Statute of the International Court of Justice is generally recognized as a definitive statement of the sources of international law.

Legal positivism

positivistlegal positivistlegal positivists
During the 19th century, it was recognized by legal positivists that a sovereign could limit its authority to act by consenting to an agreement according to the principle pacta sunt servanda.

Sovereignty

sovereignsovereign entitysovereign nation
During the 19th century, it was recognized by legal positivists that a sovereign could limit its authority to act by consenting to an agreement according to the principle pacta sunt servanda.

Pacta sunt servanda

cannot unilaterally rescindhonor our agreementspromises are made to be kept
During the 19th century, it was recognized by legal positivists that a sovereign could limit its authority to act by consenting to an agreement according to the principle pacta sunt servanda.

Contract

contract lawcontractsagreement
Treaties can play the role of contracts between two or more parties, such as an extradition treaty or a defense pact.

Extradition

extraditedextraditeextradition treaty
Treaties can play the role of contracts between two or more parties, such as an extradition treaty or a defense pact.

Legislation

legislativelegislatelegislative act
Treaties can also be legislation to regulate a particular aspect of international relations or form the constitutions of international organizations.

Jus ad bellum

Jus ad bellemJust Causes of Warlegal justification for the use of force
Some treaties are the result of codifying existing customary law, such as laws governing the global commons, and jus ad bellum.

Geneva Conventions

Geneva Conventionillegal under international lawCommon Article 3
The most obvious example is the 1949 Geneva Conventions for the Protection of War Victims.

Chapter XVI of the United Nations Charter

ARTICLE 102 of the Charter of the United NationsArticle 105 of the United Nations CharterChapter XVI, Article 103
Pursuant to Chapter XVI, Article 103 of the United Nations Charter, the obligations under the United Nations Charter overrides the terms of any other treaty.

Preamble to the United Nations Charter

Preamblepreamble to the UN Charter
Meanwhile, its Preamble affirms establishment of the obligations out of treaties and source of international law.

Opinio juris sive necessitatis

opinio jurisacceptance that such practice is required by law
Article 38(1)(b) of the ICJ Statute refers to "international custom" as a source of international law, specifically emphasizing the two requirements of state practice plus acceptance of the practice as obligatory or opinio juris sive necessitatis (usually abbreviated as opinio juris).

Comity

comitalinternational comitycomity of nations
Derived from the consistent practice of (originally) Western states accompanied by opinio juris (the conviction of States that the consistent practice is required by a legal obligation), customary international law is differentiated from acts of comity (mutual recognition of government acts) by the presence of opinio juris (although in some instances, acts of comity have developed into customary international law, i.e. diplomatic immunity).

Diplomatic immunity

immunitydiplomats immunity from arrestimmune
Derived from the consistent practice of (originally) Western states accompanied by opinio juris (the conviction of States that the consistent practice is required by a legal obligation), customary international law is differentiated from acts of comity (mutual recognition of government acts) by the presence of opinio juris (although in some instances, acts of comity have developed into customary international law, i.e. diplomatic immunity).

Persistent objector

persistent objectionstates that object
A dissenting state is entitled to deny the opposability of a rule in question if it can demonstrate its persistent objection to that rule, either as a member of a regional group or by virtue of its membership of the international community.

Peremptory norm

jus cogensius cogensnorm
Also, jus cogens (peremptory norm) is a custom, not a treaty.

United Nations Security Council

UN Security CouncilSecurity CouncilU.N. Security Council
It may be argued that the practice of international organizations, most notably that of the United Nations, as it appears in the resolutions of the Security Council and the General Assembly, are an additional source of international law, even though it is not mentioned as such in Article 38(1) of the 1946 Statute of the International Court of Justice.

United Nations General Assembly

General AssemblyUN General AssemblyGeneral Assembly of the United Nations
It may be argued that the practice of international organizations, most notably that of the United Nations, as it appears in the resolutions of the Security Council and the General Assembly, are an additional source of international law, even though it is not mentioned as such in Article 38(1) of the 1946 Statute of the International Court of Justice. The principal means of contribution to state practice for the majority of states will be at meetings of international organizations, particularly the UN General Assembly, by voting and otherwise expressing their view on matters under consideration.

Nuclear weapon

atomic bombnuclear weaponsnuclear
The fact that no nuclear weapons have been used since 1945, for example, does not render their use illegal on the basis of a customary obligation because the necessary opinio juris was lacking.