Expert Witness

Expert Witness in the United States

A person who has special knowledge of a subject matter about which he or she is to testify in a legal proceeding. An expert witness is a person who has knowledge or expertise not usually found in the average person. Educational degrees may provide the basis for a person being an expert witness, but special skill or knowledge based on experience may also qualify a person as an expert witness. Whether a person possesses the necessary qualifications to serve as an expert witness is a determination of the trial court. The testimony of an expert witness is based directly on his or her status as an expert. A lay witness, on the other hand, provides testimony based on personal knowledge of facts at issue in the case.

See Also

Witness (Civil Process).

Analysis and Relevance

Expert witnesses are crucial in particular kinds of cases. A psychiatrist, for example, is key in attempting to establish an insanity or diminished capacity defense to criminal charges. Similarly, geologists or chemists with particular expertise in water quality may be pivotal witnesses in a case where plaintiffs are seeking damages from a defendant who allegedly contaminated a water supply with discharged industrial waste. Unlike the lay witness, whose testimony is confined to what he or she knows directly about the fact situation, the expert witness can offer expert testimony. This allows the expert to offer opinions and conclusions drawn from their expertise.

Notes and References

  1. Definition of Expert Witness from the American Law Dictionary, 1991, California

Practical Information

Note: Some of this information was last updated in 1982

A person selected because of knowledge or skill to examine, estimate, and ascertain things and to make a report of his or her opinion at trial. An expert can draw from facts inferences that a layman could not make, and in this way the expert aids the jury. The facts upon which the expert’s opinion is based may have been personally observed by the expert or incorporated in a hypothetical question put to him or her. Whether a witness is qualified to speak as an expert is a preliminary question of fact to be determined by the trial court. A few examples of specialized fields where an expert’s testimony would be necessary are medicine, ballistics, chemical analysis, psychiatry, and engineering.

(Revised by Ann De Vries)

What is Expert Witness?

For a meaning of it, read Expert Witness in the Legal Dictionary here. Browse and search more U.S. and international free legal definitions and legal terms related to Expert Witness.

Pathologist as Expert Witness; Malpractice Considerations

This section examines the Pathologist as Expert Witness; Malpractice Considerations subject in its related phase of trial. In some cases, other key elements related to trials, such as personal injury, business, and criminal litigation, are also addressed.

Cause of Action for Negligence or Malpractice of Expert Witness: an Overview

This section examines this type of action. This subject identifies the various elements of the Cause of Action for Negligence or Malpractice of Expert Witness, offering a practical approach to the litigation issues of this cause of action. See also the entry about legal risks.

Expert Witness

Real Property Expert Witness Filings RP-EW-DOCS Database

This is a database related to interests in and transfers of real estate, in the following material: Case Law, Briefs, Trial Filings, and Jury Verdicts. A description of this real estate database is provided below:

Selected reports, affidavits, depositions, and transcripts of trial testimony of expert witnesses in cases from selected state and federal trial courts that relate to interests in real property. Coverage begins with 1996.

Further information on United States legal research databases, including real property databases, are provided following the former link.


Further Reading

Expert Witness: Open and Free Legal Research of US Law

Federal Primary Materials

The U.S. federal government system consists of executive, legislative, and judicial branches, each of which creates information that can be the subject of legal research about Expert Witness. This part provides references, in relation to Expert Witness, to the legislative process, the federal judiciary, and the primary sources of federal law (cases, statutes, and regulations).

Federal primary materials about Expert Witness by content types:

Laws and Regulations

US Constitution
Federal Statutory Codes and Legislation

Federal Case Law and Court Materials

U.S. Courts of Appeals
United States courts of appeals, inclouding bankruptcy courts and bankcruptcy appellate panels:

Federal Administrative Materials and Resources

Presidential Materials

Materials that emanate from the President’s lawmaking function include executive orders for officers in departments and agencies and proclamations for announcing ceremonial or commemorative policies. Presidential materials available include:

Executive Materials

Federal Legislative History Materials

Legislative history traces the legislative process of a particular bill (about Expert Witness and other subjects) for the main purpose of determining the legislators’ intent behind the enactment of a law to explain or clarify ambiguities in the language or the perceived meaning of that law (about Expert Witness or other topics), or locating the current status of a bill and monitoring its progress.

State Administrative Materials and Resources

State regulations are rules and procedures promulgated by state agencies (which may apply to Expert Witness and other topics); they are a binding source of law. In addition to promulgating regulations, state administrative boards and agencies often have judicial or quasi-judicial authority and may issue administrative decisions affecting Expert Witness. Finding these decisions can be challenging. In many cases, researchers about Expert Witness should check state agency web sites for their regulations, decisions, forms, and other information of interest.

State rules and regulations are found in codes of regulations and administrative codes (official compilation of all rules and regulations, organized by subject matter). Search here:

State opinions of the Attorney General (official written advisory opinions on issues of state law related to Expert Witness when formerly requested by a designated government officer):

Tools and Forms

Law in Other Regions

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