Trials depend on people who know something relevant. A witness is a person who provides testimony under oath in a legal proceeding about what they perceived, know, or—in the case of experts—opine based on specialized knowledge.

Fact witnesses describe observations; expert witnesses help the fact-finder understand technical matters. Witnesses may be compelled by subpoena and are subject to cross-examination. Credibility assessments drive many outcomes.

Witness intimidation and perjury are separate crimes that protect the integrity of testimony. Preparation helps witnesses understand procedure without scripting false accounts. Clear, consistent testimony remains one of the most persuasive forms of evidence.

• Person who testifies under oath in a proceeding
• May offer fact or expert evidence
• Subject to examination and cross-examination
• May be compelled by court order