Public International Law vs Private International Law: Sources, State Sovereignty and Enforcement Mechanisms

What is the Difference between Public International Law and Private International Law?

Public International Law vs Private International Law: Public International Law governs the legal relations between sovereign states and international entities. Private International Law deals with disputes between private parties that span multiple jurisdictions.

Public International Law vs Private International Law

Navigating the complex world of international law often involves encountering two seemingly similar but markedly different branches.

To someone new, they may sound alike, given their shared prefix. However, delve a little deeper, and you will find these two areas of law address wholly different aspects of international relations and legal issues.

Public International Law vs Private International Law Comparison - what is private and public international law 1

Definition and Scope of Public International Law and Private International Law

Public International Law:

  • Concerns legal relations between sovereign states and other entities granted international personality (like the United Nations).
  • Regulates the conduct of states and international entities with respect to matters such as war and peace, treaty law, sea law, international human rights, and diplomatic immunity.

Private International Law:

  • Also known as “Conflict of Laws,” it deals with the choice of applicable law and jurisdiction in cases with a foreign element.
  • Addresses disputes between private parties (individuals or corporations) that span multiple jurisdictions. For instance, which country’s law should be applied if a German citizen sues an American company?

Foundational Sources of Public International Law vs Private International Law

Public International Law:

  • Treaties and Conventions: These are formal agreements between states or international entities.
  • Customary International Law: Practices that have evolved and are accepted as law.
  • General Principles: Recognised in major legal systems and can be used as a subsidiary means for determining rules of law.
  • Judicial Decisions and Scholarly Writings: Used as subsidiary means for determining the rules of law.

Private International Law:

  • National Legislation: Countries have rules about which law applies in private international disputes.
  • Treaties: Like the Hague Conventions, which address private international law issues.
  • Case Law: Judicial decisions can influence how the rules of private international law are applied.

Principal Concerns

Public International Law:

  • State Sovereignty: Every state’s right to govern its affairs without interference
  • International Responsibility: When states breach their international obligations.
  • Territorial Integrity: Respecting the geographical boundaries of states.
  • Non-Intervention: Prohibiting interference in the internal affairs of other states.

Private International Law:

  • Choice of Law: Which country’s law applies to a given legal dispute?
  • Recognition and Enforcement: Will a judgment from one country’s court be recognised and enforced in another country?

Bodies and Institutions

Public International Law:

  • International Court of Justice (ICJ): Principal judicial organ of the UN.
  • International Criminal Court (ICC): Tries individuals for international crimes.
  • United Nations and its various organs.
  • Specialised agencies: Like the World Health Organization (WHO).

Private International Law:

  • National Courts: Each country’s court system typically handles private international law disputes.
  • Arbitration Panels: Parties might opt for arbitration in cross-border disputes.
  • The Hague Conference on Private International Law: A global intergovernmental organisation working for the “progressive unification” of the rules of private international law.
  • The International Institute for the Unification of Private Law (UNIDROIT): An intergovernmental organization dedicated to harmonising international private law across countries through uniform rules, standards, and conventions.

Impact and Enforcement

Public International Law:

  • States and international entities are subject to public international law. However, its enforcement is complex since no centralised global authority can enforce it. Often, states comply due to international pressure, diplomatic consequences, or economic sanctions.

Private International Law:

  • This often impacts individuals and corporations more directly than public international law. Enforcement of judgments is easier within a country but can be challenging internationally unless treaties facilitate this.

How Do States Ensure Compliance With Public International Law?

States ensure compliance with Public International Law through the desire for mutual respect, cooperation, and coexistence, thus driving states to honour their international commitments. Treaties, conventions, and accords, which states voluntarily enter into, create binding legal obligations.

Violating these agreements could lead to diplomatic tensions and harm a state’s reputation on the international stage.

International organisations like the United Nations also play a vital role in monitoring and ensuring adherence to international norms, often offering dialogue and dispute resolution platforms.

Economic and trade sanctions can also be imposed by states collectively against violators, serving as a deterrent to non-compliance. Peer pressure, or the desire to belong to the international community, is a potent factor.

Furthermore, customary international law, developed from consistent state practice and belief in its obligatory nature, offers another layer of normative behaviour that states are inclined to follow.

Difference Between Public International Law and Private International Law

AspectPublic International LawPrivate International Law
Nature and ScopeGoverns relations between sovereign states and international organisations.Deals with legal disputes involving private individuals, corporations, or entities that span multiple countries.
SubjectsIt mainly involves states, international organisations, and sometimes individuals.Concerns private parties such as individuals, corporations, and other non-state entities.
Sources of LawTreaties, customary international law, general principles of law, and decisions of international organisations.Conventions, treaties, domestic laws, and rules of procedure specific to cross-border legal matters.
Enforcement MechanismLacks a central enforcement authority; compliance often relies on state consent and international reputation.It may involve the enforcement of judgments in foreign jurisdictions based on international agreements or domestic laws.
FocusEmphasises peace, security, human rights, and diplomatic relations on a global scale.Focuses on resolving conflicts of laws in cross-border transactions, such as contracts, torts, and family matters.
Dispute ResolutionInternational Court of Justice (ICJ), arbitration, diplomatic negotiations, and international tribunals.Courts and legal processes of different countries, and sometimes arbitration, for resolving private disputes.
Examples of IssuesTreaty negotiations, diplomatic immunity, state responsibility, use of force, and environmental treaties.Choice of law, recognition and enforcement of foreign judgments, international contracts, and transnational commercial law.
Public vs. Private InterestsPrimarily addresses the interests of states and the international community.Balances the interests of private parties while respecting the sovereignty of different legal systems.
State SovereigntyOften involves limitations on state sovereignty for the sake of international cooperation.Balances the exercise of state sovereignty with the need for cross-border legal predictability and fairness.
Public International Law vs Private International Law

How Do National Courts Interact With The Principles Of Private International Law?

National courts frequently engage with the principles of Private International Law (PrIL) when dealing with cases that have a foreign or international element.

At the core of PrIL are questions related to jurisdiction, choice of law, and the recognition and enforcement of foreign judgments.

Firstly, when a dispute arises with ties to multiple jurisdictions, national courts must determine whether they can adjudicate the matter. This involves assessing factors like where the parties are domiciled or where the dispute occurred.

Secondly, even if the court establishes jurisdiction, it must decide which country’s substantive law applies to the case’s merits, ensuring fairness and appropriate redress.

Lastly, if a judgment is rendered in one jurisdiction, national courts in another country may be asked to recognise and enforce it.

To facilitate these interactions, many countries have treaties or conventions that provide clearer guidelines for courts, enhancing predictability and fostering international cooperation in legal matters.

How Do Customary International Practices Differ In Influence Between Public International Law And Private International Law?

Customary international practices hold a distinct and central position within Public International Law (PuIL) instead of their role in PrIL.

In PIL, customary international law emerges from consistent state practices driven by a sense of legal obligation (often termed opinio juris).

When states repeatedly act in a particular manner and believe such actions are required by international law, these practices can crystallise into binding customary rules. Notable examples include the principles of state immunity and the prohibition against the use of force.

Such customs can prevail even without treaty law and hold states accountable. Conversely, in PrIL, customary practices are less influential.

PrIL primarily revolves around determining applicable jurisdiction and law in cross-border disputes involving private parties.

While historical and consistent practices can guide decisions, PrIL is more rooted in treaties, national legislation, and judicial precedents than in evolving customary practices.

Can Corporations Be Held Liable Under Public International Law?

Historically, PuIL was primarily concerned with the conduct of states and intergovernmental entities.

However, the evolving landscape of international relations and the increasing role of multinational corporations in global affairs have prompted a reevaluation of this stance.

In modern PuIL, there’s a growing consensus that corporations can bear responsibilities, especially regarding human rights violations and environmental harms.

The most notable advancement in this realm is the United Nations Guiding Principles on Business and Human Rights (UNGPs) of 2011, emphasising corporate responsibility to respect human rights.

While the UNGPs are not legally binding, they influence corporate behaviour and state expectations. Moreover, some international criminal law instruments, like the Rome Statute of the International Criminal Court, envisage the possibility of prosecuting individuals for crimes committed on behalf of corporations, though not the corporations themselves.

Thus, while direct corporate liability in PuIL remains limited, the trajectory suggests an expanding realm of accountability for corporations in international law.


PuIL and PrIL serve as two pillars upholding the structure of international relations and cross-border issues. While they may intersect in certain scenarios, each branch has its distinct goals, methods, and areas of focus.

Understanding their differences is vital for those venturing into the vast realm of international law.

Related Articles

Notify of

Inline Feedbacks
View all comments

Join Thousands of Subscribers Who Read Our Legal Opinions And Case Analysis.