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In many states the traditional distinctions between the culpability of accomplices and principals to a crime have been replaced by statute—including the felony murder rule that may make an accomplice guilty of first degree or capital murder if he was the lookout or getaway driver for a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 Wisconsin, the law does not make a sharp distinction between the principal actor and an accomplice in the commission of a crime. Under Wisconsin Statutes, particularly section 939.05, a person is considered a party to a crime if they directly commit the offense, intentionally aid and abet the commission of it, or are a conspirator in its planning. This means that an accomplice, such as a lookout or getaway driver, is held to the same level of criminal responsibility as the person who directly commits the criminal act. Furthermore, under the state's felony murder rule, an accomplice can be charged with first-degree intentional homicide if a death occurs during the commission of a crime they were involved in, even if they were not the one who directly caused the death. This reflects the state's policy of holding all participants in a crime responsible for the outcomes of that criminal activity.