Boyle (defendant) was charged with violating the Racketeering Influence and Corrupt Organizations Act (RICO Act), 18 U.S.C. § 1963(c). He was part of a group that engaged in a series of bank robberies. The group was “loosely and informally organized.” The group did not have a leader or a hierarchy, and it seemed to define the roles for the bank robberies (e.g., driver, lookout, etc.) on an ad hoc basis. The RICO Act stated that it was “unlawful for any person employed by or associated with any enterprise engaged in, or the activities of which affect, interstate or foreign commerce, to conduct or participate, directly or indirectly, in the conduct of such enterprise’s affairs through a pattern of racketeering activity or collection of unlawful debt.” The RICO Act did not define “enterprise.” Over Boyle’s objection, the district court instructed the jury that it could “find an enterprise where an association of individuals, without structural hierarchy, form[ed] solely for the purpose of carrying out a pattern of racketeering acts.” Additionally, the district court instructed the jury that “[c]ommon sense suggests that the existence of an association-in-fact is oftentimes more readily proven by what it does, rather than by abstract analysis of its structure.” The jury convicted Boyle, and the United States Court of Appeals for the Second Circuit affirmed. Boyle petitioned for certiorari on the ground that the district court’s jury instructions improperly defined enterprise. The United States Supreme Court granted certiorari.