Law of The United States

The law of the United States consists of many levels of codified and uncodified forms of law, of which the most important is the United States Constitution, the foundation of the federal government of the United States. The Constitution sets out the boundaries of federal law, which consists of constitutional acts of Congress, constitutional treaties ratified by Congress, constitutional regulations promulgated by the executive branch, and case law originating from the federal judiciary.

The Constitution and federal law are the supreme law of the land, thus preempting conflicting state and territorial laws in the fifty U.S. states and in the territories. However, the scope of federal preemption is limited, because the scope of federal power is itself rather limited. In the unique dual-sovereign system of American federalism (actually tripartite because of the presence of Indian reservations), states are the plenary sovereigns, while the federal sovereign possesses only the limited supreme authority enumerated in the Constitution. Indeed, states may grant their citizens broader rights than the federal Constitution as long as they do not infringe on any federal constitutional rights. Thus, most U.S. law (especially the actual "living law" of contract, tort, property, criminal, and family law experienced by the majority of citizens on a day-to-day basis) consists primarily of state law, which can and does vary greatly from one state to the next.

At both the federal and state levels, the law of the United States was originally largely derived from the common law system of English law, which was in force at the time of the Revolutionary War. However, U.S. law has diverged greatly from its English ancestor both in terms of substance and procedure, and has incorporated a number of civil law innovations.