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In many states the traditional distinctions between the culpability of accomplices and principals to a crime have been replaced by statute—including the felony murder rule that may make an accomplice guilty of first degree or capital murder if he was the lookout or getaway driver for a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 Indiana, the law does not distinguish sharply between principals and accomplices in the commission of a crime. Under Indiana Code (IC 35-41-2-4), a person who knowingly or intentionally aids, induces, or causes another person to commit an offense is legally accountable for the crime as if they had committed it themselves. This means that accomplices, such as lookouts or getaway drivers, are treated as if they had committed the criminal act and can be charged and prosecuted to the same extent as the principal offender. Additionally, Indiana's felony murder statute (IC 35-42-1-1) stipulates that if a killing occurs during the commission of or attempt to commit certain felonies, including robbery, all participants in the felony can be charged with murder, regardless of their role in the underlying crime. This includes accomplices who may not have directly caused the death but participated in the felony that led to the killing.