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In many states the traditional distinctions between the culpability of accomplices and principals to a crime have been replaced by statute—including the felony murder rule that may make an accomplice guilty of first degree or capital murder if he was the lookout or getaway driver for a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 Iowa, the concept of a criminal accomplice is covered under the state's aiding and abetting laws. According to Iowa Code Section 703.1, a person who knowingly aids and abets another in the commission of a crime may be charged and punished as a principal. This means that an accomplice, such as a lookout or getaway driver in a bank robbery, can face the same charges and penalties as the person who directly commits the criminal act. Furthermore, under Iowa's felony murder rule, as outlined in Iowa Code Section 707.2, if a person is killed during the commission of a felony (such as a bank robbery), an accomplice can be charged with first-degree murder, even if they did not directly cause the death. This reflects the state's position that being an active participant in a felony that results in a death carries the highest level of criminal responsibility, equivalent to that of the person who actually commits the murder.