This article details the terrorist activities of the Japanese cult, Aum Shinrikyo, from the perspective of its complex engineering efforts aimed at producing nuclear and chemical weapons. The experience of this millenarian organization illustrates that even violent non-state actors with considerable wealth and resources at their disposal face numerous obstacles to realizing their destructive aspirations. Specifically, Aum’s attempts at complex engineering were stymied by a combination of unchecked fantastical thinking, self-imposed ideological constraints, and a capricious leadership. The chapter highlights each of these mechanisms, as well as the specific ways in which they constrained the decision-making process and the implementation of the complex engineering tasks associated with their unconventional weapons development.