It is often said that the law recognizes two bases for holding a defendant liable for a crime: (1) the fact that she committed it, or (2) the fact that she aided or abetted it. In this Dissertation, I argue that legal liability is unrecognizable as criminal liability unless it is incurred by an agent for an exercise of her own agency. Therefore, the law not only should not, but could not, hold a defendant liable for a crime otherwise than on the grounds that she committed it. When courts hold an accomplice liable for the principal’s conduct, they are indulging in a legal fiction, treating the principal’s conduct as if it were the accomplice’s. The common law was driven to adopt this legal fiction, I argue, because it struggled to understand how accomplices commit the crimes of which they are guilty. I identify and respond to four objections to the claim that accomplices commit the crimes of which they are guilty, each of which could have contributed to prompting the common law to resort to a legal fiction to secure criminal liability for accomplices. I conclude by recommending that the law roll back this legal fiction along with the mistake(s) that prompted it and summarizing how this would affect the scope of accomplice liability.