In U.S. law, Giglio information or material refers to material tending to impeach the character or testimony of the prosecution witness in a criminal trial.
The Supreme Court's 1963 decision in Brady v. Maryland, 373 U.S. 83 (U.S. 1963) held that the prosecution violates due process when it "withholds evidence on demand of an accused which, if made available, would tend to exculpate him or reduce the penalty.
In Giglio v. United States, 405 U.S. 150, 153 (U.S. 1972), the Supreme Court extended the prosecution's obligations under Brady to disclosure of impeachment evidence. Supreme Court clarified that all impeachment evidence, even if not a prior statement by a witness falls within the Brady rule. Giglio mandated that the prosecution should disclose any and all information that may be used to impeach the credibility of prosecution witnesses including law enforcement officers. Impeachment information under Giglio includes information such as prior criminal records or other acts of misconduct of prosecution witness, promises of leniency or immunity offered to prosecution witnesses.