A History of Double Criminality in Extradition

This article sets out the history of double criminality in the law of extradition. It shows how that it only emerged as a legal requirement in the 'Jay Treaty, the 1794 treaty between the US and UK. The article explores how the 'Jay proviso', a procedural requirement that the requesting state produce sufficient evidence to satisfy the requested state of the criminality of the requested person, morphed through interaction between common law and civil law states into a substantive requirement that the acts for which extradition is requested be criminal under the laws of both states. The article diccusses the evolution of the idea, and of its rationale, and then concludes that acceptance of this idea by the early part of the 20th Century confirmed its status as a general principle of law, or perhaps even a rule of customary international law.