A criminal accomplice is a person who knowingly, voluntarily, or intentionally assists another person in the commission of a crime—or under some circumstances, a person who fails to prevent another person from committing a crime. Unlike a person who aids and abets a crime by helping with the planning of the crime but is often not present at the scene of the crime—and unlike an accessory after the fact, who is not present at the scene of the crime but assists after the commission of the crime to help the perpetrator avoid arrest or punishment—an accomplice actively participates in the commission of the crime. For example, a person who acts as a lookout or getaway driver for a bank robbery is an accomplice.

In many states the traditional distinctions between the culpability of accomplices and principals to a crime have been replaced by statute—including the felony murder rule that may make an accomplice guilty of first degree or capital murder if he was the lookout or getaway driver for a bank robbery that resulted in a death.

In Arizona, an individual who assists in the commission of a crime is considered an accomplice and is subject to criminal liability. Under Arizona law, an accomplice is someone who, with the intent to promote or facilitate the commission of a crime, knowingly provides any means or opportunity for another to commit the offense. This includes actions taken before, during, or after the crime that aid, counsel, agree to aid, or attempt to aid in planning or committing the crime. The state does not make a significant distinction between the principal actor and the accomplice; both can be charged and punished to the same extent as if they had directly committed the offense themselves. Regarding the felony murder rule, if a death occurs during the commission of a felony, such as a bank robbery, an accomplice can be charged with first-degree murder, even if their role was limited to being a lookout or getaway driver. This reflects the state's approach to holding all participants in a felony that results in death equally responsible for the homicide.