Definition
Ex relatu (abbreviated ex rel.) is a Latin phrase meaning "on the relation of" or "upon the information of." It designates the private party — the relator — at whose instigation and in whose interest a legal action is brought by a public officer or the state. The phrase appears most often in the formal caption of a case where a government official (such as an attorney general) nominally brings suit but acts on behalf of, and at the prompting of, a named private individual or organization.
The structure is typically rendered as: State ex rel. [Relator's Name] v. [Defendant]. The government entity holds nominal plaintiff status; the relator is the real party in interest driving the litigation.
Common Language
Ex relatu has no meaningful counterpart in ordinary modern or historical English usage. It is Latin legal vocabulary with no common-language analog. This section is omitted accordingly.
Common Confusion
Ex rel. is sometimes misread as indicating that the named individual is a defendant or a minor party. In fact, the relator is the functional plaintiff — the party whose grievance animates the suit. Researchers should not confuse this with in re (concerning a matter or estate), which signals a proceeding not framed as adversarial between named parties, or with ex parte (on one side only), which signals a proceeding conducted without notice to or participation by the opposing party. All three Latin prefixes appear in case captions, but they signal entirely different procedural postures.
Why It Matters in Research
Case caption reading. Searches for cases involving a particular relator may fail if a researcher searches only on the nominal government plaintiff. In older reporters and digests, indexing practices varied — some indexed by the government entity, others by the relator's name, and some by both. A search strategy should anticipate both.
Qui tam and statutory relator actions. The ex rel. form is the standard caption for qui tam suits under the False Claims Act, in which a private whistleblower (relator) brings suit in the government's name to recover funds defrauded from the federal treasury. Understanding ex relatu is therefore a prerequisite for navigating qui tam research. The government's decision whether to intervene in a qui tam action materially affects the proceeding, but the caption structure — government ex rel. relator — remains the same regardless.
State attorney general practice. State AG offices regularly bring consumer protection, antitrust, and civil rights actions ex rel. a complainant or the people. Caption conventions differ by state: some jurisdictions use "People ex rel.," others "State ex rel.," and a few "Commonwealth ex rel." These are functionally equivalent but require adjusted search terms.
Historical equity and prerogative writ practice. In older equity and common law courts, ex rel. was the standard form for relator actions seeking prerogative writs — mandamus, quo warranto, and information in the nature of quo warranto. Burrill's citation to Reg. Orig. 34, 36, 42 reflects this: the Register of Original Writs was the foundational writ-practice source in English common law, and these page references place ex relatu squarely in the procedural context of writ applications. Researchers working in pre-twentieth-century state court records should expect to encounter the phrase in mandamus and quo warranto proceedings, often in contexts that have no direct modern analog.
Corpus navigation tip. In Law Mind's historical corpus, ex rel. actions appear both as standalone entries and embedded in broader writ or equity proceedings. Cross-referencing against quo warranto and mandamus entries will surface cases that a caption-only search may miss.
Historical Dictionary Support
Burrill's Law Dictionary gives a terse but accurate entry: "On the relation, or information," citing the Registrum Omnium Brevium (Register of Original Writs) at pages 34, 36, and 42. The citation is consistent with the phrase's origins in English writ practice, where a relator's information was the procedural trigger for the Crown's issuance of certain prerogative writs. Burrill does not develop the relator's procedural role beyond this, reflecting the assumption in nineteenth-century legal practice that practitioners would understand the writ context without elaboration.
No other historical dictionary in the present source set covers ex relatu separately. The phrase's substantive legal content is better captured in treatises on pleading and practice than in general legal dictionaries of the period, which typically treated it as a well-understood term of art requiring only translation.
What historical sources miss: the modern qui tam dimension. The False Claims Act relator action is a twentieth-century development (with significant expansion after 1986 amendments) that Burrill and contemporaneous sources could not anticipate. Researchers should not rely on historical dictionary entries alone when the research concern is whistleblower or false claims litigation.
Jurisdictional Note
Caption conventions for ex rel. actions vary by state. "State ex rel." is the most common American form; "People ex rel." is standard in California, Illinois, and New York; "Commonwealth ex rel." appears in Pennsylvania and a handful of other states. Federal qui tam cases universally use "United States ex rel." Researchers moving between jurisdictions should adjust search terms accordingly.
Encyclopedia Cross-Reference
Constitutional Law: Ex parte Young — The Fiction That Permits Suits Against State Officers (constitutional_42). Many ex rel. actions in state court raise related questions about sovereign immunity and the fiction of suits nominally brought by or against government officers; the Ex parte Young doctrine is the federal analog and useful comparative context.
Intellectual Property: The Defend Trade Secrets Act — Federal Civil Action and Ex Parte Seizure (ip_94). Relevant for researchers encountering ex parte seizure orders, which share caption and procedural complexity with ex rel. practice, though they are distinct mechanisms.