Voir dire (/ˈvwɑːr dɪər/ ^ⓘ; often /vɔɪr daɪər/;^{[citation needed]} from an Anglo-Norman term in common law meaning "to speak the truth") is a legal term for procedures during a trial that help a judge decide certain issues:

From Old French voir "true" (from Latin verus "true," from PIE root *were-o- "true, trustworthy") and from Old French dire "to say" (from Latin dicere "speak, tell, say," from PIE root *deik- "to show," also "pronounce solemnly").

It originally referred to an oath taken by jurors to tell the truth (Latin: verum dicere). It comes from the Anglo-Norman language.

In earlier centuries, a challenge to a particular juror would be tried by other members of the jury panel, and the challenged juror would take an oath of voir dire, meaning to tell the truth. This procedure fell into disuse when the function of trying challenges to jurors was transferred to the judge.

In England and Wales, Cyprus, Hong Kong, Ireland, Australia, New Zealand, Papua New Guinea and Canada, it refers to a "trial within a trial". It is a hearing to determine the admissibility of evidence, or the competency of a witness or juror. As the subject matter of the voir dire often relates to evidence, competence or other matters that may lead to bias on behalf of the jury, the jury may be removed from the court for the voir dire.

Under Scots law, jury selection is random, and there are a few well-defined exclusions in criminal trials.

In Canada, the case of Erven v. The Queen holds that testimony on a voir dire cannot influence the trial itself. This remains true even if the judge ruled against the accused in the voir dire. The judge is assumed to ignore what they heard during voir dire. The jury is never present during a voir dire. However, since the evidence given at a voir dire may be redundant to evidence at trial, with the consent of the parties a procedure called a "blended voir dire" may be used to save time. In this procedure, evidence given in the voir dire, if then found admissible, is transferred into the main trial without having to be repeated.

In Australia, the rule about voir dire is in section 189 of the Evidence Act 1995 (Cth): "On a voir dire parties can call witnesses, cross-examine opponent's witnesses and make submissions- as they might in the trial proper." The term has thus been broadened in Australian jurisdictions to include any hearing during a trial where the jury is removed. The High Court of Australia has noted that the voir dire is an appropriate forum for the trial judge to reprimand counsel or for counsel to make submissions as to the running of the court to the trial judge.