After Internal Revenue Service investigations exposed widespread fraud among tax shelter promoters, angry investors sued for securities fraud under Securities and Exchange Commission Rule 10b-5, which provides a cause of action against “primary violators” of the Rule but not against mere “aiders and abettors.” This controversial distinction is further complicated by the recent introduction of “scheme liability” lawsuits under two previously obscure provisions of Rule 10b-5. This Note examines the circuit split over the “primary violator”/“aider and abettor” distinction in scheme liability claims, arguing that the circuits’ conflicting concepts of scheme liability actually cover similar conduct, and that tax shelter promoters likely will be considered primary violators under either concept.