The Double Jeopardy Clause of the Fifth Amendment to the U.S. Constitution provides that a person may not be tried again for the twice for the same crime once they are acquitted. This is known as "Double Jeopardy." Double jeopardy attaches to a charge after a jury is empaneled, a judge in a "bench trial" begins to hear evidence, a jury has made a decision, or if a person pleads guilty to the crime. The purpose of double jeopardy is to prevent the government from potentially abusing its power to repeatedly charge a person with the same crime, from the same set of facts, until they get the result they want.

In practice, strict application of this principle in a criminal context may produce injustices. In England, several murderers went free because the needed evidence wasn't discovered until after their acquittal. The British Parliament responded by enumerating circumstances under which a retrial could be ordered (U.K. Criminal Justice Act 2003).

Since the U.S. has a federal system, both the federal government and state governments have independent sovereign authority to define and prosecute crimes under their separate jurisdictions. Thus, while a defendant cannot be prosecuted twice for the same crime in a single state, if the crime also violates the laws of a different state or the federal government, double jeopardy does not attach and the defendant can be tried in that state or under federal law.

Since the U.S. has a federal system, both the federal government and state governments have sovereignty over their citizens and can prosecute crimes against them independently, even if the defendant was acquitted by the other. For example, let's say you are a high ranking campaign official and you have been secretly working for a foreign power for a decade. During that time you laundered the money this foreign power paid you to avoid paying taxes. This is a federal crime under federal anti-money laundering statutes and federal tax law. However, this same act is also a state crime under state anti-money laundering statutes and state tax law. So, even if you are tried in a federal court and found Not Guilty of all of these charges you can still be tried again for the same acts in state court because the state criminal charges are different than the federal criminal charges.

An important case in defining the limits of double jeopardy is U.S. v. Felix (1992), which held that someone charged for conspiracy is not protected by double jeopardy from also being charged for the offenses that were conspired.

For more information on how a federal pardon affects double jeopardy, see this article from Jed Handelsman Shugerman.