First adopted in 1975, the Federal Rules of Evidence codify the evidence law that applies in United States Federal courts. In addition, many states in the United States have either adopted the Federal Rules of Evidence, with or without local variations, or have revised their own evidence rules or codes to at least partially follow the federal rules.
The law of evidence governs the proof of facts and the inferences flowing from such facts during the trial of civil and criminal lawsuits. Before the twentieth century, evidence law was largely the product of decisional law. During the twentieth century, projects such as the California Evidence Code and the Uniform Rules of Evidence encouraged the codification of those common law evidence rules. In 1965, Chief Justice Earl Warren appointed an advisory committee of fifteen to draft the new rules. The committee was composed of lawyers and legal scholars from across the country.
The Federal Rules of Evidence began as rules proposed pursuant to a statutory grant of authority, the Rules Enabling Act, but were eventually enacted as statutory law.
Rules of evidence govern whether, when, how, and for what purpose, proof of a legal case may be placed before a trier of fact for consideration.
Prevailing in court requires a good understanding of the rules of evidence in the given venue. The rules vary depending upon whether the venue is a criminal court, civil court or family court, and they vary by jurisdiction. One reason to have a lawyer, among others, is that he or she should be familiar with the rules of evidence. If one were allowed simply to tell the court what one knew to be the truth, and how one knew it, one might prevail. However, the rules of evidence may prohibit one from presenting one's story just as one likes.
Some important rules involve relevance, privilege, witnesses, opinions, expert testimony, hearsay, authenticity, identification and rules of physical evidence.
The rules of evidence were developed over several centuries and are based upon the rules from Anglo-American common law brought to the New World by early settlers. Their purpose is to be fair to both parties, disallowing the raising of allegations without a basis in provable fact. They are sometimes criticized as a legal technicality, but are an important part of the system for achieving a just result.