The Common Law of England is in general the basis of the law of all the states of the American Union except Louisiana, whose system is based upon the Civil or Roman Law. In most of the states it is provided that the English Common Law and English Statutes relative to private law up to the beginning of the fourth year of James I (March 24, 1606), with a few exceptions, shall be accepted as law in the state. The system of Equity Jurisprudence is accepted in these states along with the Common Law. In every state the common or unwritten law must, of course, give way to the state's constitution and statutes.

The United States, as such, has no Common law.

Strictly speaking the only Federal law is that of the United States Constitution and statutes. The Federal Courts, however, in many cases apply the laws of the state in which the court sits, and thus indirectly are governed by the Common Law.