Criminal law in the united states presents a diversity and complexity that is not encountered in any other modern legal system. This chapter addresses only a few significant aspects of American criminal law that resonate with some of the noteworthy characteristics of the American legal system in general, such as American federalism, American constitutionalism, and American systems of court procedures.

At the outset, it should be noted that criminal law, like virtually all American public law, is now completely statutory. This was not, however, always the case. In the early years of the American republic, the elements of many crimes were defined by prior judicial decisions, as was the law of criminal evidence and procedure. For instance, the first criminal case brought before the newly constituted District Court for the District of Maine in 1790 was a common law prosecution of an individual who had seized a small sailing ship and murdered the captain. The defendant was prosecuted under the federal common law of piracy, which the court discerned from tradition and reports of prior judicial decisions, largely in England. Based on this case law, the defendant was convicted by a jury and duly hanged.

The common law of crimes remained viable in the United States until the mid or later part of the nineteenth century. Even as American states commenced to identify crimes and punishments by statute, the common law continued to play a major role in fleshing out the legislation.