Definition
A Latin phrase meaning "according to what is just and good" or "in justice and fairness." When a court, arbitral tribunal, or other adjudicatory body is empowered to decide ex aequo et bono, it is authorized to resolve a dispute on the basis of equity and conscience rather than by strict application of existing legal rules. The decision-maker is freed from the obligation to follow positive law and may instead fashion a result that seems fair given the particular circumstances of the case.
The concept operates most prominently in international arbitration, where parties may expressly grant a tribunal authority to decide ex aequo et bono in lieu of — or as a supplement to — a governing body of national or international law. Outside that context, the phrase appears in jurisprudential writing as shorthand for equity-based reasoning as a method of adjudication.
---
Common Confusion
Ex aequo et bono is sometimes conflated with general equitable principles or with the doctrine of amiable compositeur, a related but distinct concept from civil law and international arbitration. An amiable compositeur is also freed from strict legal rules but is typically understood to retain some obligation to consider applicable law as a starting point before departing from it, while a tribunal acting purely ex aequo et bono may disregard positive law entirely from the outset. Researchers should not treat these as synonyms, especially in international arbitration materials where the distinction can affect the scope of a tribunal's authority and the reviewability of its award.
---
Why It Matters in Research
The phrase is largely dormant in Anglo-American common law sources but alive and consequential in international arbitration and public international law. Researchers working in those areas should know several things:
First, the phrase appears in foundational international instruments. The Statute of the International Court of Justice (Art. 38(2)) expressly permits the ICJ to decide a case ex aequo et bono if the parties agree — though this power has never been formally invoked by the ICJ, making doctrine on it sparse and largely theoretical.
Second, in international commercial and investment arbitration, major institutional rules (ICSID, ICC, UNCITRAL) allow parties to confer ex aequo et bono authority on tribunals by agreement. Researchers reviewing arbitral awards should check whether the tribunal was operating under a governing law clause or under ex aequo et bono authority, because this affects how the award's reasoning should be read and how it can be challenged.
Third, the phrase appears in older treatises on private international law and conflict of laws as part of broader discussions of equity's role in legal systems derived from Roman and civil law traditions. When encountered in those sources, it signals a jurisprudential argument rather than a procedural mechanism.
Fourth, common law sources from the 18th and 19th centuries occasionally use the phrase in equity jurisprudence to describe the Chancellor's jurisdiction. Blackstone's usage (3 Bl. Comm. 163, the source Black's 2nd cites) is representative: the phrase signals a broad equitable mandate, not a formal procedural category. Researchers should not read that usage back into modern international arbitration doctrine without care.
---
Historical Dictionary Support
Black's Law Dictionary (2nd Ed.) provides a serviceable gloss — "in justice and fairness; according to what is just and good; according to equity and conscience" — and correctly traces the phrase to civil law origins with a citation to Blackstone. The entry is brief and reflects the phrase's limited footprint in the common law sources that Black's primarily served.
What the historical dictionaries collectively miss is the phrase's twentieth-century transformation into a technical term of international arbitration practice. The early editions of Black's, Bouvier, and similar American dictionaries treat the phrase as a piece of Latin legal vocabulary describing an equitable disposition — useful in rhetorical or jurisprudential contexts — rather than as a defined procedural mechanism with jurisdictional implications. Researchers relying solely on those sources will have the correct core meaning but will lack any sense of how the phrase functions as a grant of authority in modern dispute resolution instruments.
---
Jurisdictional Note
In domestic U.S. courts, the phrase has no operative procedural significance and appears mainly in historical or scholarly discussion. Its practical importance is concentrated in international arbitration and proceedings before international tribunals, where it functions as a defined term of art with consequences for tribunal jurisdiction and award review. Civil law systems have a richer historical relationship with the concept through the amiable compositeur tradition, and researchers working with French, Swiss, or other continental arbitration materials will encounter the two concepts in closer proximity than in common law sources.
---