Nullum crimen, nulla poena sine praevia lege poenali

Nulla poena sine lege (Latin for "no penalty without a law") is a legal principle, requiring that one cannot be punished for doing something that is not prohibited by law. This principle is accepted and codified in modern democratic states as a basic requirement of the rule of law. It has been described as "one of the most 'widely held value-judgement[s] in the entire history of human thought'".

In modern European criminal law, e.g. of the Constitutional Court of Germany, the principle of nulla poena sine lege has been found to consist of four separate requirements:

One complexity is the lawmaking power of judges under common law. Even in civil law systems that do not admit judge-made law, it is not always clear when the function of interpretation of the criminal law ends and judicial lawmaking begins.

In English criminal law there are offences of common law origin. For example, murder is still a common law offence and lacks a statutory definition. The Homicide Act 1957 did not include a statutory definition of murder (or any other homicidal offense). Therefore, the definition of murder was the subject of no fewer than six appeals to the House of Lords within the next 40 years (Director of Public Prosecutions v. Smith [1961] A.C. 290; Hyam v. Director of Public Prosecutions [1975] A.C. 55; Regina v. Cunningham [1982] A.C. 566; Regina v. Moloney [1985] A.C. 905; Regina v. Hancock [1986] A.C. 455; Regina v. Woollin [1998] 4 A11 E.R. 103 (H.L.)).

The question of jurisdiction may sometimes come to contradict this principle. For example, customary international law allows the prosecution of pirates by any country (applying universal jurisdiction), even if they did not commit crimes at the area that falls under this country's law. A similar principle has appeared in the recent decades with regard to crimes of genocide (see genocide as a crime under domestic law); and UN Security Council Resolution 1674 "reaffirms the provisions of paragraphs 138 and 139 of the 2005 World Summit Outcome Document regarding the responsibility to protect populations from genocide, war crimes, ethnic cleansing and crimes against humanity" even if the State in which the population is being assaulted does not recognise these assaults as a breach of domestic law. However, it seems that universal jurisdiction is not to be expanded substantially to other crimes, so as to satisfy Nulla poena sine lege.

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