Definition
Interference is a multi-context legal term describing unlawful or actionable obstruction of another party's recognized legal right, relationship, or protected interest. Its meaning shifts substantially depending on the area of law in which it appears.
(1) Patent law. A proceeding — formerly an administrative process within the U.S. Patent and Trademark Office — to determine priority of invention when two or more applicants claim substantially the same patentable subject matter. The interference resolved which party was the first to invent, and thus entitled to the patent. This proceeding was a defining feature of the U.S. first-to-invent patent system.
(2) Tort law. The intentional or tortious disruption of another's legally protected relationship or interest. Principal subtypes include intentional interference with contract (inducing a breach of an existing contract) and intentional interference with prospective economic advantage (disrupting an anticipated business relationship). Liability generally requires intent, knowledge of the relationship, and causation of actual harm.
(3) Family law. Unlawful obstruction of a parent's custodial or visitation rights, including conduct by the other parent, third parties, or — in more serious cases — the removal of a child across jurisdictional lines. May be treated as a civil wrong, a criminal offense, or both depending on the jurisdiction and the nature of the conduct.
(4) General usage. In broader legal contexts, interference may describe any unauthorized meddling with another's property, rights, or legal proceedings — including interference with a witness, interference with commerce, or interference with contractual performance.
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Common Language
Modern common usage (Wiktionary): The act of interfering; obstruction or meddling in another's affairs.
Historical common usage (Webster's 1913): The act or state of interfering; a meddlesome intrusion in the business of others; also, the mutual influence of two physical waves (light, sound) producing characteristic phenomena.
The common meaning tracks the legal meaning loosely but misses the specificity that matters in legal research. In law, interference is not merely meddling — it is actionable conduct directed at a legally cognizable interest. The patent law sense, in particular, is entirely technical and has no ordinary-language parallel. Researchers encountering "interference" in historical legal materials must determine which legal context governs before the term becomes useful.
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Common Confusion
The term "interference" covers distinct doctrines that share a name but little else. Patent interference (a priority dispute between inventors) has nothing in common procedurally or substantively with tortious interference (a civil wrong against a contracting party) or custodial interference (a family law and criminal law concept). Historical sources, especially older dictionaries, tend to define the term solely in its patent context, which can mislead researchers working in tort or family law. Additionally, tortious interference with contract and tortious interference with prospective economic advantage are closely related but not identical — the latter involves a more speculative interest and typically requires a higher showing of improper conduct.
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Recognized Forms
/SUBTYPES
Patent Interference: A USPTO proceeding under the pre-America Invents Act (AIA) first-to-invent system to determine priority between competing claimants. Replaced after 2011 by the derivation proceeding under the first-inventor-to-file system.
Tortious Interference with Contract: An intentional tort requiring existence of a valid contract, the defendant's knowledge of it, intentional inducement of breach, actual breach, and resulting damages.
Tortious Interference with Prospective Economic Advantage (also: Prospective Business Relations): Similar to the above but targeting anticipated — not yet existing — economic relationships. Elements vary by jurisdiction, with some requiring independently wrongful conduct beyond mere intent.
Custodial Interference: Obstruction of court-ordered custody or visitation rights. Ranges from civil contempt to criminal prosecution depending on the severity and whether the child is removed across state or national lines.
Interference with a Witness / Obstruction: Federal and state statutes criminalize interference with witnesses, jurors, or court officers as a category of obstruction of justice. Treated separately from civil interference torts.
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Why It Matters in Research
The historical dictionaries are heavily skewed toward the patent sense. Researchers using Black's 1st or 2nd Edition, or Bouvier's, will find patent interference treated as the primary — in some entries, the only — legal meaning. This reflects the 19th-century importance of patent interference proceedings in American jurisprudence. Do not assume that a historical source's silence on tortious interference means the tort did not exist; it did, but was typically discussed under headings like "malicious interference" or folded into broader treatment of tort liability.
The patent interference proceeding is now largely obsolete for applications filed after March 16, 2013 (the AIA's first-inventor-to-file provisions). Researchers working with patent records from before that date will encounter interference proceedings extensively; those working with post-AIA materials will not. The distinction is a significant research trap for anyone conflating the two regimes.
In tort law, the elements of tortious interference vary meaningfully across jurisdictions. Some states require that the defendant's conduct be independently tortious or criminal; others require only improper purpose or improper means. Corpus-wide searches on "interference" in tort materials should be filtered by jurisdiction before drawing conclusions about the required elements.
In family law, custodial interference sits at the intersection of civil contempt, state criminal codes, the Uniform Child Custody Jurisdiction and Enforcement Act (UCCJEA), and federal law (the Parental Kidnapping Prevention Act). Historical materials will rarely use the phrase "custodial interference" — look instead for "abduction," "detention," and custody contempt proceedings.
The Law Mind corpus connects interference across multiple encyclopedias. Researchers moving between patent, tort, and family law contexts should treat these as distinct doctrinal threads that happen to share a term.
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Historical Dictionary Support
Black's Law Dictionary (both editions) defines interference exclusively in the patent context, framing it as a "collision between rights claimed or granted." This was the dominant legal usage of the term in 19th- and early 20th-century American legal writing. The 2nd Edition adds case citations clarifying that "strictly speaking" an interference requires overlapping claims — indicating that courts of the era were already wrestling with the term's precise limits.
Bouvier's redirects entirely to the patents entry, offering no independent analysis. Rapalje & Lawrence and Anderson's Dictionary of Law do not address interference at all in their provided excerpts, instead covering adjacent terms (interest, interim). This silence is itself informative: by the late 19th century, the tort law dimensions of interference were not yet sufficiently systematized to warrant dedicated dictionary treatment.
The Webster's 1913 definition captures the physical science sense (wave interference) alongside the colloquial sense of meddling — neither of which maps cleanly onto the legal doctrine. The absence of the tortious interference framework from both the legal and lay dictionaries of this era reflects that the tort, while recognized in case law, had not yet consolidated into the structured elements-based doctrine that modern practice applies.
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Jurisdictional Note
Tortious interference with prospective economic advantage varies significantly across U.S. states: some require that the defendant's conduct be independently wrongful (beyond mere intentional interference), while others do not. Custodial interference is criminalized in all U.S. jurisdictions but under varying statutory definitions and penalty levels. Patent interference as a USPTO proceeding applies only to applications governed by pre-AIA law.
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Encyclopedia Cross-Reference
Intentional Torts — Property and Economic — Intentional Interference with Contract (The Law Mind Torts & Personal Injury Encyclopedia)
Family Law — Interference with Parental Rights (Custodial Interference, Alienation) (The Law Mind Family Law Encyclopedia)
Child Custody — Interference with Custody and Parental Kidnapping (The Law Mind Family Law Encyclopedia)
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