Expert witness
Expert witness: A witness qualified by knowledge, skill, experience, training or education to testify in the form of an opinion or otherwise. Under Federal Rule of Evidence 702, the proponent must show the court it is more likely than not that the expert's knowledge will help the trier of fact, the testimony rests on sufficient facts or data and reliable methods, and the expert's opinion reliably applies those methods to the facts of the case.
What expert witness means
In practice, you will see expert witness in pleadings, motions, orders and court rules. The definition above explains the general meaning. Even so, the meaning can shift with context. Therefore, always read it alongside the rule or document where it appears.
Where expert witness comes up
For example, the term appears in these procedures:
- Initial Disclosures (Fed. R. Civ. P. 26(a)(1)): information each party must share without being asked, such as people likely to have discoverable information and documents it may use.
Read the source: Witness.
How to research the term
Start with the primary source. For example, if expert witness appears in a federal rule, read the rule itself and its official notes. After that, check your court’s local rules and any standing orders from the judge. In addition, search recent decisions from your own state or federal district. They show how courts read expert witness in practice. Because state rules often differ, our state procedures guide links to each state’s official rules. Above all, make sure the version you read is still in force.
You can read the official rule text online for free.
Related legal terms
- Discovery: the pretrial process in which parties obtain information and evidence from each other and from nonparties.
- Initial disclosures: basic information each party must provide early in a federal case without waiting for a discovery request.
- Ex post facto law: latin for "after the fact." A law that applies to the past in a way the Constitution forbids: it makes criminal an act that was innocent when done, aggravates a crime, increases the punishment after the fact, or changes the rules of evidence to make conviction easier for a past act (Calder v.
- Excusable neglect: a standard courts use to decide whether to excuse a missed deadline or mistake, considering the circumstances.
Why precise terms matter
Courts read legal terms closely. As a result, knowing the exact meaning of a word helps you follow orders, rules and filings. Each glossary entry on Lawtopolis is short on purpose and links to the pages where the term is used.
Sources
Sources last reviewed: 2026-10-24
Lawtopolis provides legal information and education, not legal advice. Using this site does not create an attorney-client relationship. Laws and court rules vary by jurisdiction and change over time; verify every authority against the official source and consult a licensed attorney in your jurisdiction about your situation.