The law of evidence, also known as the rules of evidence, encompasses the rules and legal principles that govern the proof of facts in a legal proceeding. These rules determine what evidence must or must not be considered by the trier of fact in reaching its decision. The trier of fact is a judge in bench trials, or the jury in any cases involving a jury. The law of evidence is also concerned with the quantum (amount), quality, and type of proof needed to prevail in litigation. The rules vary depending upon whether the venue is a criminal court, civil court, or family court, and they vary by jurisdiction.

The quantum of evidence is the amount of evidence needed; the quality of proof is how reliable such evidence should be considered. Important rules that govern admissibility concern hearsay, authentication, relevance, privilege, witnesses, opinions, expert testimony, identification and rules of physical evidence. There are various standards of evidence, standards showing how strong the evidence must be to meet the legal burden of proof in a given situation, ranging from reasonable suspicion to preponderance of the evidence, clear and convincing evidence, or beyond a reasonable doubt.

There are several types of evidence, which vary from one another in form or source.

Evidence governs the use of testimony (e.g., oral or written statements, such as an affidavit), exhibits (e.g., physical objects), documentary material, or demonstrative evidence, which are admissible (i.e., allowed to be considered by the trier of fact, such as jury) in a judicial or administrative proceeding (e.g., a court of law).

When a dispute, whether relating to a civil or criminal matter, reaches the court there will always be a number of issues which one party will have to prove in order to persuade the court to find in their favour. The law must ensure certain guidelines are set out in order to ensure that evidence presented to the court can be regarded as trustworthy.

Hammurabi's Code had some evidence requiring an oath and witness. See specifically laws 10, 11, and 12.

The Old Testament demanded at least two witnesses for conviction of a crime.

Ancient Roman law allowed freedom to judges to evaluate evidence, but insisted that "proof is incumbent on the party who affirms a fact, not on him who denies it" and "no-one should be convicted on suspicion". Medieval Roman law developed an elaborate grading of degrees of evidence. Building on the Biblical two-witness rule, it concluded that a single witness, or private documents, could constitute half-proof, which though insufficient for conviction might justify torture to extract further evidence. Because evidence in the continental (civil law) system was evaluated by judges rather than juries, that system did not develop exclusionary rules of evidence in the way English law did.