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In many states the traditional distinctions between the culpability of accomplices and principals to a crime have been replaced by statute—including the felony murder rule that may make an accomplice guilty of first degree or capital murder if he was the lookout or getaway driver for a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 Colorado, the legal concept of a criminal accomplice is covered under the state's complicity statute. According to Colorado law, a person is considered an accomplice if they intentionally aid, abet, advise, or encourage the principal before or during the commission of a crime. This means that an accomplice is criminally liable to the same degree as the person who actually commits the crime. For instance, if someone acts as a lookout or a getaway driver during a bank robbery, they can be charged with the same offenses as the person who physically robs the bank. Colorado law also includes the felony murder rule, which can result in an accomplice being charged with first-degree murder if a death 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 state's statutes effectively eliminate the distinction between the principal and the accomplice, holding both parties equally responsible for the crime committed.