In Blockburger v. U.S., the U.S. Supreme Court rules that the double jeopardy clause is not violated when a defendant is convicted of two different crimes arising from a single act. The defendant was convicted under two federal laws for making a single sale of morphine to a single customer: selling a drug separately from its original packaging and selling it without a prescription. The Court rules that because the two crimes require proof of different “elements,” they should not be considered the same crime, and therefore, two convictions can result. The “same elements” test – i.e., if two crimes require proof of the same elements, then double jeopardy prevents prosecution of a defendant for both crimes – is one of the most enduring principles in the interpretation of the double jeopardy provision.