In common law, a foundation is sufficient preliminary evidence of the authenticity and relevance for the admission of material evidence in the form of exhibits or testimony of witnesses. Material evidence is important evidence that may serve to determine the outcome of a case. Exhibits include real evidence, illustrative evidence, demonstrative evidence, and documentary evidence. The type of preliminary evidence necessary to lay the proper foundation depends on the form and type of material evidence offered.

The lack of foundation is a valid objection that an adverse party may raise during trial.

Materiality is the significance of facts to the matter at hand.

In the law of evidence.

An item of evidence is said to be material if it has some logical connection to a fact of consequence to the outcome of a case. Materiality, along with probative value, is one of two characteristics that make a given item of evidence relevant. This largely depends on the elements of the cause of action the plaintiff seeks to prove, or that the prosecutor must prove in a criminal case to secure a conviction. Which issues must be factually proven are therefore a product of the underlying substantive law.

Public policy doctrines for the exclusion of relevant evidence, in the law of evidence in the United States, encompass several types of evidence that would be relevant to prove facts at issue in a legal proceeding, but which are nonetheless excluded because of public policy concerns. There are five major areas of exclusion that arise out of the Federal Rules of Evidence ("FRE"): subsequent remedial measures, ownership of liability insurance, offers to plead guilty to a crime, offers to settle a claim, and offers to pay medical expenses. Many states have modified versions of the FRE under their own state evidence codes which widen or narrow the public policy exclusions in state courts.

The exclusionary rule, under which evidence gathered by the police from an illegal search is excluded, is of similar operation but is typically considered separately.

Tampering with evidence, or evidence tampering, is an act in which a person alters, conceals, falsifies, or destroys evidence with the intent to interfere with an investigation (usually) by a law-enforcement, governmental, or regulatory authority. It is a criminal offense in many jurisdictions.

Tampering with evidence is closely related to the legal issue of spoliation of evidence, which is usually the civil law or due process version of the same concept (but may itself be a crime). Tampering with evidence is also closely related to obstruction of justice and perverting the course of justice, and these two kinds of crimes are often charged together. The goal of tampering with evidence is usually to cover up a crime or with intent to injure the accused person.