The law cannot make all men equal， but they are all equal before the law.
—Frederick Pollock （British jurist）
英美法系和大陆法系一般被认为是当今世界最重要的两大法律体系。美国与大多数英联邦国家都继承了英国法律的普通法传统。一小部分在独立战争时期实行的重要的英国成文法几乎一字不差地被美国各州照搬。但独立之后，美国法庭却很少追随英联邦判例，除非没有相应的美国判例、案情和法律条文等。美国联邦法是源于宪法赋予国会的权力为某些特定目的而制定并颁布的适用于全国的法律。几乎所有的法律都被编入《美国法典》。美国的五十个州都是独立的主权实体，拥有自己的州宪法和州政府。它们保留制定除联邦宪法、联邦法律和联邦参议院批准的国际条约规定之外的任何法律的全部权力。各州同时还将立法权授予数千个政府部门、区、县、城市与特区。
Law of the United States
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， the supreme law of the land， under the Constitution s Supremacy Clause， is the United States Constitution， as well as laws enacted by Congress， and treaties to which the U.S. is a party. The Constitution forms the basis for federal laws under the federal constitution in the United States； it circumscribes the boundaries of the jurisdiction of federal law along with the laws in the fifty U.S. states and in the territories.
Sources of law
In the United States， the law is derived from four sources. These four sources are constitutional law， statutory law， administrative regulations， and the common law（ which includes case law） . The most important source of law is the United States Constitution. All other law falls under and is subordinate to that document. No law may contradict the Constitution. For example， if Congress enacts a statute that conflicts with the Constitution， the Supreme Court may find that law unconstitutional and declare it invalid.
Notably， a statute does not disappear automatically merely because it has been found unconstitutional； it must be deleted by a subsequent statute. Many federal and state statutes have remained on the books for decades after they were ruled to be unconstitutional. However， under the principle of stare decisis， no sensible lower court will enforce an unconstitutional statute， and any court that does so will be reversed by the Supreme Court. Conversely， any court that refuses to enforce a constitutional statute（ where such constitutionality has been expressly established in prior cases） will risk reversal by the Supreme Court.
American common law
The United States and most Commonwealth countries are heirs to the common law legal tradition of English law； for example， U.S. courts have inherited the principle of stare decisis.
English law was formally“received”into the United States in several ways. First， all U.S. states except Louisiana have enacted“reception statutes”which generally state that the common law of England （ particularly judge-made law） is the law of the state to the extent that it is not repugnant to domestic law or indigenous conditions. Some reception statutes impose a specific cutoff date for reception， such as the date of a colony s founding， while others are deliberately vague. Thus， contemporary U.S. courts often cite pre-Revolution cases when discussing the evolution of an ancient judge-made common law principle into its modern form， such as the heightened duty of care traditionally imposed upon common carriers.
Second， a small number of important British statutes in effect at the time of the Revolution have been independently reenacted by U.S. states. Two examples that many lawyers will recognize are the Statute of Frauds and the Statute of 13 Elizabeth （ the ancestor of the Uniform Fraudulent Transfers Act） . Such English statutes are still regularly cited in contemporary American cases interpreting their modern American descendants.
However， it is important to understand that despite the presence of reception statutes， much of contemporary American common law has diverged significantly from British Commonwealth common law. The reason is that although the courts of the various Commonwealth nations are often influenced by each other s rulings， American courts rarely follow post-Revolution Commonwealth rulings unless there is no American ruling on point， the facts and law at issue are nearly identical， and the reasoning is strongly persuasive.
Early on， American courts， even after the Revolution， often did cite contemporary English cases. This was because appellate decisions from many American courts were not regularly reported until the mid-19th century； lawyers and judges， as creatures of habit， used English legal materials to fill the gap. But citations to English decisions gradually disappeared during the 19th century as American courts developed their own principles to resolve the legal problems of the American people. The number of published volumes of American reports soared from eighteen in 1810 to over 8， 000 by 1910. Foreign law has never been cited as binding precedent， but merely as a reflection of the shared values of Anglo-American civilization or even Western civilization in general.
Federal law
Federal law originates with the Constitution， which gives Congress the power to enact statutes for certain limited purposes like regulating interstate commerce. Nearly all statutes have been codified in the United States Code. Many statutes give executive branch agencies the power to create regulations， which are published in the Federal Register and codified into the Code of Federal Regulations. Regulations generally also carry the force of law under the Chevron doctrine. Many lawsuits turn on the meaning of a federal statute or regulation， and judicial interpretations of such meaning carry legal force under the principle of stare decisis.