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In many states the traditional distinctions between the culpability of accomplices and principals to a crime have been replaced by statute—including the felony murder rule that may make an accomplice guilty of first degree or capital murder if he was the lookout or getaway driver for a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 Pennsylvania, the concept of an accomplice is codified under the state's criminal statutes. An individual is considered an accomplice if they intentionally aid, agree to aid, or attempt to aid another person in planning or committing a crime. Pennsylvania law does not make a sharp distinction between the principal actor and the accomplice; both can be charged and punished to the same extent for the crime committed. This means that an accomplice to a felony can face the same penalties as the person who directly engaged in the criminal act. Furthermore, under Pennsylvania's felony murder rule, an accomplice can be charged with first-degree murder if a killing occurs during the commission of a felony such as a bank robbery, even if the accomplice's role was limited to being a lookout or getaway driver. The law recognizes that by aiding in the crime, the accomplice has contributed to the criminal act and therefore shares responsibility for its outcomes.