Dual criminality in extradition is the rule that a country will only surrender a person if the conduct they are accused of would be a crime in both the requesting country and the country being asked. Under most modern treaties, the offense must also be serious enough to carry at least one year of imprisonment in each jurisdiction. The principle keeps a person from being handed over for behavior that is perfectly legal where they live, and it grounds the entire extradition process in a shared understanding of what counts as criminal.
What the Rule Actually Requires
The threshold question is simple to state: would the accused person’s conduct be punishable as a crime in both countries? If the answer is no, extradition cannot proceed for that offense. The idea reflects a basic fairness principle. A country should not lend its law enforcement machinery to punish someone for acts its own laws treat as lawful.1U.S. Department of State Foreign Affairs Manual. 7 FAM 1610 Introduction
In the United States, this analysis only happens when a valid treaty is in place. Federal extradition law, 18 U.S.C. § 3181, ties the entire extradition chapter to “the existence of any treaty of extradition with such foreign government.”2Office of the Law Revision Counsel. 18 USC 3181 – Scope and Limitation of Chapter Once a treaty exists, 18 U.S.C. § 3184 authorizes any federal judge or magistrate judge to issue a warrant, hold a hearing, and decide whether the charged offense falls within the treaty’s coverage.3Office of the Law Revision Counsel. 18 USC 3184 – Fugitives From Foreign Country to United States
How U.S. Courts Test Dual Criminality
American courts take a conduct-based approach. A judge does not care whether both countries call the crime the same thing, or whether the two statutes have identical elements. The Supreme Court settled this in Collins v. Loisel (1922), holding that “the law does not require that the name by which the crime is described in the two countries shall be the same; nor that the scope of the liability shall be coextensive.” What matters is whether “the particular act charged is criminal in both jurisdictions.”
In practice, the judge reads the narrative of what the person allegedly did and asks whether those actions would violate any domestic criminal statute. A foreign charge labeled “unlawful enrichment” might find its match in domestic fraud or embezzlement statutes. An allegation of “economic sabotage” might correspond to theft or destruction of property. The labels do not control; the behavior does.
Tax cases show how this works. Different countries structure their tax codes differently, and the technical elements of tax fraud vary widely. Courts applying Collins v. Loisel look past those differences to the underlying conduct: did the person hide income, file false returns, or use fraudulent schemes to avoid paying taxes? If so, dual criminality is satisfied even though the foreign statute looks nothing like the Internal Revenue Code.
Offenses That Commonly Fail the Test
Some categories of conduct routinely fail dual criminality in the United States because the First Amendment or other constitutional protections make the behavior lawful here. Blasphemy is a criminal offense in some countries but protected speech in the United States. The same holds for offenses like adultery, apostasy, or certain forms of political dissent that are criminalized abroad but carry no criminal penalty domestically. When the requesting country’s charge rests on conduct that American law affirmatively protects, extradition cannot proceed.
Purely fiscal offenses have a more nuanced history. Many older treaties excluded tax crimes entirely, reflecting a traditional reluctance to enforce another country’s revenue laws. More recent U.S. treaties have moved away from that blanket exclusion, so tax offenses increasingly qualify for extradition when dual criminality is otherwise satisfied.1U.S. Department of State Foreign Affairs Manual. 7 FAM 1610 Introduction
How Treaties Frame the Question
Not every extradition treaty handles covered offenses the same way. Older treaties used a list approach, naming every specific crime (murder, robbery, forgery, and so on) for which extradition would be granted. If an offense was not on the list, it was not extraditable, no matter how serious. The obvious problem was that new types of crime such as cybercrime, identity theft, and money laundering kept outpacing the lists, forcing constant renegotiation.1U.S. Department of State Foreign Affairs Manual. 7 FAM 1610 Introduction
Modern U.S. treaties replace that rigid list with the dual criminality standard. Instead of matching offense names, the treaty asks whether the conduct would be punishable by at least one year of imprisonment under the laws of both countries. That formula automatically covers new crimes as legislatures create them, without needing to amend the treaty.1U.S. Department of State Foreign Affairs Manual. 7 FAM 1610 Introduction
One boundary worth noting: the European Union took a different path with the European Arrest Warrant. For 32 categories of serious offenses (including terrorism, trafficking, and corruption), the warrant eliminates the dual criminality check entirely, as long as the crime carries at least three years of imprisonment in the issuing country.4United Nations Office on Drugs and Crime. Organized Crime Module 11 Key Issues: Extradition The United States is not part of that system, but it shows how different regions balance sovereignty against efficient cooperation.
When Extradition Can Still Be Denied
Even if dual criminality is clearly met, several treaty-based grounds can still block a surrender. These are deliberate policy choices about the limits of international cooperation, not technicalities.
Political Offense Exception
Most extradition treaties include an exception for political offenses, on the theory that a country should not help another government punish political dissidents. In U.S. courts, determining whether an act qualifies as a “political offense” falls to the judge reviewing the request. If the judge finds the offense political in nature, extradition is denied even if the conduct would otherwise be criminal in both jurisdictions.1U.S. Department of State Foreign Affairs Manual. 7 FAM 1610 Introduction
Recent treaties have narrowed this exception considerably. Violent crimes, genocide, and terrorism are specifically carved out, so a person cannot invoke the political offense defense for bombing a civilian target even during a genuine political uprising.
Military Offenses
Conduct that is criminal only under military law, such as desertion, insubordination, or absence without leave, is generally not extraditable. The key distinction is whether the offense would also be a crime under ordinary civilian criminal law. A soldier who commits murder has committed a crime under both military and civilian law, so extradition remains available. A soldier who goes AWOL has committed a purely military offense, and extradition for that alone would be denied.5United Nations Office on Drugs and Crime. Revised Manuals on the Model Treaty on Extradition
Lapse of Time and Prior Prosecution
Extradition may also be refused if the statute of limitations has expired under the laws of either the requesting or the requested country, or if the accused has already been convicted or acquitted of the same conduct in the requested country. These provisions guard against stale prosecutions and protect against double jeopardy.1U.S. Department of State Foreign Affairs Manual. 7 FAM 1610 Introduction
The Rule of Specialty: The Companion Principle
Dual criminality controls whether a person can be extradited. The rule of specialty controls what happens after they are surrendered. Under this principle, the requesting country may only prosecute or punish the person for the specific offenses listed in the extradition order. Adding charges after surrender is not permitted without permission from the country that handed the person over.1U.S. Department of State Foreign Affairs Manual. 7 FAM 1610 Introduction
Specialty appears in virtually all extradition treaties. Without it, a country could file a narrow request for a relatively minor offense, then pile on far more serious charges once the person is in custody and beyond the protection of the surrendering country’s courts.
Exceptions are narrow. A country may prosecute for offenses committed after the person was extradited, and a person who voluntarily remains in the requesting country after serving their sentence or being acquitted generally loses the specialty protection. Federal prosecutors who want to bring additional charges against someone already extradited must work through the Department of Justice’s Office of International Affairs to request a formal waiver of specialty from the surrendering country.6Justice Manual. International Extradition and Related Matters
The person being prosecuted can sometimes raise a specialty violation in court, though federal courts are split on whether defendants have standing to do so. Some courts say only the surrendering country, as the treaty partner, can complain about a breach. Others allow the defendant to raise the issue directly.