State law (United States)

[9] The diversity of U.S. state law first became a notable problem during the late 19th-century era known as the Gilded Age, when interstate commerce was nurtured by then-novel technologies like the telegraph, the telephone, the steamship, and the railroad.

[14] In contrast, in jurisdictions with uncodified statutes, like the United Kingdom, determining what the law is can be a more difficult process.

For example, when the UK decided to create a Supreme Court of the United Kingdom, lawmakers had to identify every single Act referring to the House of Lords that was still good law, and then amend all of those laws to refer to the Supreme Court.

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.

Efforts by various organizations to create uniform acts to be adopted by multiple states have been made but only partially successful.

Upon its founding in 1923, ALI promptly launched its most ambitious and well-known enterprise: the creation of Restatements 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.

This means that state courts (especially at the appellate level) can and have deviated from Restatement positions on a variety of issues.

[19] Puerto Rico, a former Spanish colony, is also a civil law jurisdiction of the United States.

[21][22] 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 is Spanish.

[24] 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.

[24] 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.

Many of the western states, including California, Colorado, New Mexico, Texas, and Wyoming use a system of allocating water rights known as the prior appropriation doctrine, which is derived from Spanish civil law.