Two decades after the attacks of 9/11, preventing and countering terrorism continues to be one of the main challenges faced by policy makers. The threat of nuclear terrorism, however, is often dismissed as unlikely or not imminent. The mere circumstance that it seems unthinkable does not mean it should not be actively prevented. In fact, there are both examples of threats and feasible pathways to conduct nuclear terrorism. Therefore, countering it can no longer be met with ignorance or negligence.