Admissible evidence, in a court

Court

A court is a form of tribunal, often a governmental institution, with the authority to adjudicate legal disputes between parties and carry out the administration of justice in civil, criminal, and administrative matters in accordance with the rule of law...

 of law

Law

Law is a system of rules and guidelines which are enforced through social institutions to govern behavior, wherever possible. It shapes politics, economics and society in numerous ways and serves as a social mediator of relations between people. Contract law regulates everything from buying a bus...

, is any testimonial, documentary, or tangible evidence

Evidence (law)

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 can be considered by the trier of fact in reaching its decision and, sometimes, the weight that may be given to that evidence...

 that may be introduced to a factfinder—usually a judge

Judge

A judge is a person who presides over court proceedings, either alone or as part of a panel of judges. The powers, functions, method of appointment, discipline, and training of judges vary widely across different jurisdictions. The judge is supposed to conduct the trial impartially and in an open...

 or jury

Jury

A jury is a sworn body of people convened to render an impartial verdict officially submitted to them by a court, or to set a penalty or judgment. Modern juries tend to be found in courts to ascertain the guilt, or lack thereof, in a crime. In Anglophone jurisdictions, the verdict may be guilty,...

—in order to establish or to bolster a point put forth by a party to the proceeding. In order for evidence to be admissible, it must be relevant

Relevance (law)

Relevance, in the common law of evidence, is the tendency of a given item of evidence to prove or disprove one of the legal elements of the case, or to have probative value to make one of the elements of the case likelier or not. Probative is a term used in law to signify "tending to prove."...

, without being prejudicial, and it must have some indicia of reliability.

Relevance

For evidence to be relevant, it must tend to prove or disprove some fact that is at issue in the proceeding. However, if the utility of this evidence is outweighed by its tendency to cause the factfinder to disapprove of the party it is introduced against for some unrelated reason, it will not be admissible. Furthermore, certain public-policy considerations bar the admission of otherwise relevant evidence.

Reliability

For evidence to be reliable enough to be admitted, the party proffering the evidence must be able to show that the source of the evidence makes it so. If the evidence is in the form of witness

Witness

A witness is someone who has firsthand knowledge about an event, or in the criminal justice systems usually a crime, through his or her senses and can help certify important considerations about the crime or event. A witness who has seen the event first hand is known as an eyewitness...

 testimony, the party introducing the evidence must lay the groundwork

Lay a foundation

In 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...

 for the credibility of the witness, and his knowledge of the things to which he attests. Hearsay

Hearsay

Hearsay is information gathered by one person from another person concerning some event, condition, or thing of which the first person had no direct experience. When submitted as evidence, such statements are called hearsay evidence. As a legal term, "hearsay" can also have the narrower meaning of...

 is generally barred for its lack of reliability. If the evidence is documentary, the party proffering the evidence must be able to show that it is authentic, and must be able to demonstrate the chain of custody

Chain of custody

Chain of custody refers to the chronological documentation or paper trail, showing the seizure, custody, control, transfer, analysis, and disposition of evidence, physical or electronic...

 from the original author to the present holder. The trial judge performs a "gatekeeping" role in excluding unreliable testimony. The United States Supreme Court first addressed the reliability requirement for experts in the landmark case Daubert v. Merrell Dow Pharmaceuticals, Inc. 509 U.S. 579 (1993). The Court laid out four non-exclusive factors that trial courts may consider when evaluating scientific expert reliability: (1) whether scientific evidence has been tested and the methodology with which it has been tested; (2) whether the evidence has been subjected to peer review or publication; (3) whether a potential rate of error is known; and (4) whether the evidence is generally accepted in the scientific community. Id. at 592-94. Kumho Tire Co., Ltd. v. Carmichael later extended the Daubert analysis to include all expert testimony. 526 U.S. 137 (1999).