In theUnited States,state law refers to thelaw of each separateU.S. state.
The fifty states are separatesovereigns,[1] with their ownstate constitutions,state governments, andstate courts. All states have alegislative branch which enacts state statutes, an executive branch that promulgates state regulations pursuant to statutory authorization, and a judicial branch that applies, interprets, and occasionally overturns both state statutes and regulations, as well as local ordinances. States retain the power to make laws covering anything not otherwise preempted by thefederal Constitution, federal statutes, or international treaties ratified by thefederal Senate. Normally,state supreme courts are the final interpreters of state institutions and state law, unless their interpretation itself presents a federal issue, in which case a decision may be appealed to theU.S. Supreme Court by way of a petition for writ ofcertiorari.[2] State courts regularly haveconcurrent jurisdiction with federal courts and, where applicable, apply or are also bound by federal law. State laws have dramatically diverged in the centuries since independence, to the extent that the United States cannot be regarded as one legal system (as to the majority of types of law traditionally under state control), but instead as 50separate systems oftort law,family law,property law,contract law,criminal law, and so on.[3]
In the United States, most cases are litigated in state courts and involve claims and defenses under state laws.[4][5] In a 2018 report, theNational Center for State Courts' Court Statistics Project found that state trial courts received 83.8 million newly filed cases in 2018, which consisted of 44.4 million traffic cases, 17.0 million criminal cases, 16.4 million civil cases, 4.7 million domestic relations cases, and 1.2 million juvenile cases.[6] In 2018, state appellate courts received 234,000 new cases (appeals).[6] By way of comparison, all federal district courts in 2016 together received only about 274,552 new civil cases, 79,787 new criminal cases, and 833,515 bankruptcy cases, while federal appellate courts received 53,649 new cases (appeals).[7]
The law of most of the states is based on thecommon law of England; the notable exception isLouisiana, whose civil law is largely based uponFrench andSpanish law. The passage of time has led to state courts and legislatures expanding, overruling, or modifying the common law; as a result, the laws of any given state invariably differ from the laws of its sister states. Thus, as noted above, the U.S. must be regarded as 50separate systems of tort law, family law, property law, contract law, criminal law, and so on.[3] (In addition, theDistrict of Columbia and thefederal territories also have their own separate legal systems analogous to state legal systems, although they do not enjoy state sovereignty.)
A typical example of the diversity of contemporary state law is the legal test for finding aduty of care, the first element required to proceed with a lawsuit fornegligence (the basis for mostpersonal injury lawsuits). A 2011 article found that 43 states use a multifactorbalancing test usually consisting of four to eight factors, but there are 23 various incarnations because so few states use exactly the same test, and consolidating those into a single list results in 42 unique factors.[8] Naturally, the laws of different states frequently come into conflict with each other, which has given rise to a huge body of law regulating theconflict of laws in the United States. As of the mid-2010s, American federal and state courts were deciding around 5,000 conflict-of-laws cases each year—far more than in any other country or even any other continent.[9]
The diversity of U.S. state law first became a notable problem during the late 19th-century era known as theGilded Age, wheninterstate commerce was nurtured by then-novel technologies like thetelegraph, thetelephone, thesteamship, and therailroad. Many lawyers during the Gilded Age complained about how the diversity and volume of state law hampered interstate trade and introduced complexity and inconvenience into virtually any interstate transaction (commercial or otherwise).[10] This widespread frustration was evident at the founding of theAmerican Bar Association in 1878; one of the ABA's original founding purposes was to promote "uniformity of legislation throughout the Union."[11] There have been three major reactions to this problem, none of which were completely successful: codification, uniform acts, and the Restatements.

The United States, with the exception ofLouisiana, originally inherited a common law system[12] in which the law was not organized and restated such that it could be identified as (1) relevant to a particular legal question and (2) currently in force. The process of organizing the law, called codification, was borrowed from the civil law through the efforts of American lawyerDavid Dudley Field.[13] Field, in turn, was building upon early (but wholly unsuccessful) foundational work by the English legal philosopherJeremy Bentham, who actually coined the verb "to codify" for the process of drafting a legal code.[14] The earliest attempt at codification occurred inMassachusetts with a 1648 publication.[12]
Naturally, there is much diversity in the structure of the state codes, reflecting the diversity of the statutory law on which they were built.New York's codes are known as "Laws".California andTexas simply call them "Codes". Other states use terms such as "Code of [state name]", "Revised Statutes", or "Compiled Statutes" for their compilations. California, New York, and Texas use separate subject-specific codes; Maryland'scode has, as of 2016, been completely recodified from numbered articles into named articles; virtually all other states and the federal government use a single code divided into numbered titles or other top-level divisions. Louisiana is a unique hybrid in that it has five subject-specific codes and a set of Revised Statutes for everything else. A poorly drafted 1864 anti-corruption amendment to Pennsylvania's constitution prevented its legislature from starting comprehensive codification until 1970 (after the state constitution was finally amended to add the necessary exception in 1967).[15]
The word "codification" as used inAmerican English can be very confusing, especially to lawyers from outside of the United States. In some contexts, especially the codes created by Field and his allies, the word was applied to codification in the traditional European sense of actually revising the substance of the law to make a better legal system―which necessarily meant abolition of some old rules in favor of entirely new ones. But "codification" was also applied to what should more properly be called "compilation"—merely arranging existing statutory law into a coherent structure to make the law easier to find, and sometimes "choosing sides between two pieces of contradictory legislation", but also expressly disclaiming authority to change statutory provisions with respect to matters of substance.[16]
The advantage of codification is that once thestate legislature becomes accustomed to writing new laws as amendments to an existing code, the code will usually reflect democratic sentiment as to what the current law is.[14] However, one must still review case law to determine how judges have actually interpreted and applied a particular codified statute.[17]
In contrast, in jurisdictions with uncodified statutes, like theUnited Kingdom, determining what the law is can be a more difficult process. One has to trace back to the earliest relevant Act of Parliament, and then identify all later Acts which either amended the earlier Act or expressly or impliedly repealed it. For example, when the UK decided to create aSupreme Court of the United Kingdom, lawmakers had to identify every single Act referring to theHouse of Lords that was still good law, and then amend all of those laws to refer to the Supreme Court.[18]
In most U.S. states, certain areas of the law, especially the law of contracts and torts, continue to exist primarily in the form of case law, subject only to limited statutory modifications and refinements. Thus, for example, there is no statute in most states which one can consult for answers on basic issues like the essential elements of a contract. Rather, one must consult case law, with all the complexity and difficulty that implies. The failure of most states to implement comprehensive codification of their substantive law is generally attributed toJames C. Carter, the leading 19th-century opponent of Field's codification proposals.[14][19][20]
Major exceptions include the states of California, Montana, North Dakota, and South Dakota as well as the territory of Guam, all of which largely enacted Field's proposed civil code even though it was repeatedly rejected and never enacted by his home state of New York. Idaho partially enacted the contract portions of Field's civil code but omitted the tort sections.[21] Georgia initiated its own full codification independent of Field, which resulted in the enactment of the oldest ancestor of the modernOfficial Code of Georgia Annotated in 1861. As Field belatedly conceded in an 1889 article, Georgia's code was enacted before his civil code, but he was unaware of the Georgia codification project because of the breakdown in interstate communications that preceded theAmerican Civil War.[22]
In some states, codification is often treated as a mererestatement of the common law, to the extent that the subject matter of the particular statute at issue was covered by some judge-made principle at common law. California is notorious for a confused approach to the interpretation and application of codified statutes: "California judges wandered between expansive construction and traditional strict construction, lingering at every point in between—sometimes all in the course of the same opinion."[14] In other states, there is a tradition of strict adherence to the plain text of the codes.
Efforts by various organizations to createuniform acts to be adopted by multiple states have been made but only partially successful. The two leading organizations are theAmerican Law Institute (ALI) and theUniform Law Commission (ULC), formerly known as the National Conference of Commissioners on Uniform State Laws (NCCUSL).
Uniform acts are proposed by private organizations like ULC to cover areas of law traditionally governed by the states where it would be useful to have a consistent set of rules across the various states. The most successful and influential uniform acts are theUniform Commercial Code (a joint ALI-ULC project) and theModel Penal Code (from ALI).
However, uniform acts can only become the law of a state if they are actually enacted by the state legislature. Many uniform acts have never been taken up by state legislatures, or were successfully enacted in only a handful of states, or enacted in part, thereby limiting their uniformity function.
Upon its founding in 1923, ALI promptly launched its most ambitious and well-known enterprise: the creation ofRestatements of the Law which are widely used by lawyers and judges throughout the United States to simplify the task of identifying and summarizing the current status of the common law. Instead of listing long, tedious citations of old cases that may not fit very well together (in order to invoke the long-established principles supposedly contained in those cases), or citing a treatise which may reflect the view of only one or two authors, they can simply cite a Restatement section (which is supposed to reflect the consensus of the American legal community) to refer to a particular common law principle.
The Restatements are often followed by state courts on issues of first impression in a particular state because they correctly state the current trend followed by most states on that issue. However, the Restatements are merely persuasive authority. This means that state courts (especially at the appellate level) can and have deviated from Restatement positions on a variety of issues.
Much ofLouisiana law is derived from French and Spanish civil law, which stems from its history as a colony of both France and Spain.[23]Puerto Rico, a former Spanish colony, is also acivil law jurisdiction of the United States.[24] However, the criminal law of both jurisdictions has been necessarily modified by common law influences and the supremacy of the federal Constitution.[25][26]
Furthermore, Puerto Rico is also unique in that it is the only U.S. jurisdiction in which the everyday working language of court proceedings, statutes, regulations, and case law isSpanish.[27] All states, the federal government, and most territories useAmerican English as their working language.[28] Some states, such as California, do provide certain court forms in other languages (Chinese, Korean, Spanish, Vietnamese) for the convenience of immigrants and naturalized citizens.[29] But American law as developed through statutes, regulations, and case law is always in English, attorneys are expected to take and pass thebar examination in English, judges hear oral argument, supervise trials, and issue orders from the bench in English, and testimony and documents originating in other languages are translated into English before being incorporated into the official record of a case.[28]
Many states in the southwest that were originally Mexican territory have inherited several unique features from the civil law that governed when they were part of Mexico. These states includeArizona, California,Nevada,New Mexico, and Texas. For example, these states all have acommunity property system for the property ofmarried persons (Idaho,Washington, andWisconsin have also adopted community property systems, but they did not inherit them from a previous civil law system that governed the state).[30][31] Another example of civil law influence in these states can be seen in theCalifornia Civil Code, where the law of contracts is treated as part of thelaw of obligations.
Many of thewestern states, including California,Colorado, New Mexico, Texas, andWyoming use a system of allocatingwater rights known as theprior appropriation doctrine, which is derived from Spanish civil law.[32] Each state has modified the doctrine to suit its own internal conditions and needs.[33]
{{cite journal}}: CS1 maint: multiple names: authors list (link)Unlike in civil law countries, the Code is only the starting point. The ultimate decision rests with the courts, and the courts are responsible for interpreting the code. So no matter what the code says, you must also look to cases to develop your guidance to the client.