Nullum crimen sine lege is Latin for "no crime without law." The phrase reflects the principle in criminal law and international criminal law that a person cannot or should not face criminal punishment except for an act that was criminalized by law before they performed the act. This idea is also manifested in laws that require criminal acts to be publicized in unambiguous statutory text.
In case law, the phrase appears in Justice Douglas’s concurring opinion on Hirota v. MacArthur (1949), where Douglas wrote “the maxim nullum crimen sine lege is not a limitation of sovereignty, but is in general a principle of justice. To assert that it is unjust to punish those who in defiance of treaties and assurances have attacked neighboring states without warning is obviously untrue…” to explain that the concept limited unjust application of criminal laws to defendants but would not prevent Japanese government officials from being held guilty for war crimes by the International Military Tribunal for the Far East.
Nullum crimen sine lege is sometimes called the legality principle and is also interchangeable with "nullum poena sine lege," which translates to "no punishment without law." The phrase is often also used in connection with ex post facto laws.
[Last updated in August of 2023 by the Wex Definitions Team]