Maritime security within customary international law is a significant aspect of global maritime governance, as it provides guidance and norms for addressing security threats at sea based on established state practice and legal principles. Here's an overview of maritime security in customary international law: State Practice and Opinio Juris is a Customary international law emerges from the consistent and general practice of states (state practice) coupled with a belief that such practice is legally obligatory (opinio juris). A State practice regarding maritime security includes actions taken by states to protect their maritime interests, such as patrolling territorial waters, combating piracy, and enforcing maritime regulations.

Freedom of Navigation is a Customary international law recognizes the principle of freedom of navigation, which allows vessels to traverse international waters without interference, subject to certain limitations such as innocent passage through territorial seas. States have consistently adhered to this principle through their actions and policies, reinforcing its customary status. The right of self-defence is a well-established principle of customary international law that applies to maritime security. States have the inherent right to use force, including military action, to defend themselves against imminent threats or attacks, including those occurring at sea.

Piracy and Armed Robbery is a Customary international law recognizes the universal jurisdiction of states to prosecute and punish piracy, a crime that has long been considered a threat to maritime security. States have cooperated and coordinated efforts to combat piracy and armed robbery at sea, reflecting a customary practice of mutual assistance in addressing maritime security threats. Hot pursuit is a customary practice whereby a state's law enforcement vessels may pursue and apprehend a vessel engaged in illegal activities, such as smuggling or piracy, into the territorial waters of another state.

Customary international law allows for hot pursuit under specific conditions, including immediate and continuous pursuit, notification to the coastal state, and cessation upon entry into the coastal state's territorial sea. Non-State Actors is a Customary international law increasingly addresses maritime security threats posed by non-state actors, such as terrorist organizations, criminal syndicates, and insurgent groups. States have developed customary practices, such as intelligence-sharing agreements and joint maritime patrols, to counter these threats and uphold maritime security.

Environmental Protection is a While not traditionally considered a security issue, environmental protection at sea has become an integral aspect of maritime security within customary international law. States have recognized the importance of preserving marine ecosystems and preventing environmental degradation through customary practices such as regulating pollution, controlling shipping emissions, and combating illegal fishing. maritime security in customary international law encompasses a range of principles, practices, and norms derived from state practice and consensus. By adhering to these customary rules and obligations, states contribute to maintaining safety, stability, and order in the global maritime domain.

Treaties and customary international law make up international law. States' actions taken out of a sense of legal obligation constitute customary international law. States adopt new and distinct legal standards depending on their perception of the law controlling developing situations, and treaty regimes change with time, resulting in changes to international law. The development of the law of the sea has been greatly aided by customary international law and, more recently, treaty law.

Article 89 of the LOSC states unequivocally that no State may legitimately claim sovereignty over any portion of the high seas. Secondly, the liberty of the high seas entails the liberty of actions undertaken there. This follows naturally from the fact that no State's national authority extends to the high seas. As a result, every State is entitled to the same degree of freedom to use the high seas in accordance with international law.

In Article 38(1)(b) of the statute of the International Court of Justice identifies "international custom, as evidence of a general practice accepted by law" to be a source of international law.

The Court, whose function is to decide in accordance with international law such disputes as are submitted to it, shall apply:

1. international conventions, whether general or particular, establishing rules expressly recognized by the contesting states;
2. international custom, as evidence of a general practice accepted as law;
3. the general principles of law recognized by civilized nations;
4. subject to the provisions of Article 59, judicial decisions and the teachings of the most highly qualified publicists of the various nations, as subsidiary means for the determination of rules of law.

This provision shall not prejudice the power of the Court to decide a case ex aequo et bono, if the parties agree thereto.
The Restatement (Third) on the Foreign Relations of the United States provides a good explanation of what is meant by this provision that encapsulates the overall concept as expressed by scholars and experts in the field. Section 102 and its accompanying notes explain that the custom must result from a general and consistent practice of states that is followed out of a sense of legal obligation (opinion juris sive necessitates).

This is generally interpreted to meant that there is:
Widespread repetition of the practice
by a significant number of states (the corollary to this means that the practice cannot be rejected by a significant number of states if it is to be considered custom under international law)
And has not been rejected by a substantial number of states:
The sources used to substantiate a custom are broad and result from careful study. Custom can be evidenced by treaties, resolutions and declarations of intergovernmental organizations, diplomatic materials, and other official statements from sovereign nations including legislation and case opinions.

As customary international law was known at the time it was drafted, the U.S. Constitution refers to the "Law of Nations" and includes treaties as part of "the supreme law of the land." International custom is legally binding and remains regarded as such even though it evolves. A customary norm is observed because it is thought to be binding rather than because it has been explicitly agreed to by a state; its binding force is independent of the individual's or the state's permission. Nevertheless, not every custom is explicitly agreed to by a state. Two factors are considered in determining customary international law: opinion juris and state practice. According to the International Court of Justice, "the acts in question must not only amount to a settled practice, but they also must be such, or be carried out in such a way, as to be evidence of a belief that this practice is rendered legally binding." The Court answered was if the equidistance principle was, at the date of the ruling, a customary international law binding on all States.

The Court argued that it is indeed possible for Conventions, while only contractual in origin, to pass into the corpus of international law and thus to become binding for States that have never become parties to the Convention required by the existence of a legal regulation making it necessary. Customary practice does not necessarily mean that a state's actions must be accepted by all states. All that is required is for a representative sample of States that can engage in the activity to practice it universally and consistently. States' actions demonstrate state practice. To exclude any inadvertent State practice and concentrate exclusively on what States intend to do, the justification behind a state's activities is also taken into consideration.

Exactly defining customary international law might be challenging. It can be difficult to say when an international custom has altered and when, if at all, a state's disregard for international custom turns into a new custom or just a legal infraction. Codification of customary international law inside treaty frameworks facilitates its demonstration. According to the Third Restatement on Foreign Relations Law, "international agreements can contribute to the growth of customary international law as they constitute practice of States. Six If a treaty embodies an international custom, then, generally speaking, even non-party States are bound by the standard outlined in the custom.