The law 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 and, sometimes, the weight that may be given to that evidence. The law of evidence is also concerned with the quantum (amount), quality, and type of proof needed to prevail in litigation.

The quantum of evidence is the amount of evidence needed; the quality of proof is how reliable such evidence should be considered. This includes such concepts as hearsay, authentication, admissibility, reasonable doubt, and clear and convincing evidence.

There are several types of evidence, depending on the 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).