An overt act, in the context of criminal law, is an action which might be innocent itself but if part of the preparation and active furtherance of a crime, can be introduced as evidence of a defendant's participation in a crime. Although the mere contemplation or intention to commit a crime is insufficient to convict a person of a criminal attempt, conspiracy or treason, a manifestation of such an intent by an overt act is sufficient.
The overt act required to charge someone with an attempted crime goes beyond preparatory steps and is a direct movement toward the commission of the offense. For example, a purchase of matches with the intent to burn a haystack is not an attempt to commit arson, but it is an attempt to commit arson to applying a burning match to a haystack, even if no fire results. The overt act need not be the last act essential to the consummation of the offense.