Nuclear terrorism is an absolutely terrifying but unobservable phenomenon. Given that there has never been an actual terrorist incident involving nuclear weapons, disagreement exists over how seriously we should take the threat of nuclear terror. Intelligence experts believe that a determined terrorist group is capable of acquiring and transporting nuclear weapons to the target state. Declassified documents have also confirmed that US Defense Intelligence Agency (DIA) and other security agencies were afraid of the possibility of a nuclear terrorist attack at such high-profile events as the 2009 swearing-in-ceremony of President Obama and the 2010 Winter Olympics in Vancouver. Yet, many academic experts tend to dismiss nuclear terrorism as an ‘exaggerated threat’, alluding to a number of strategic and moral constraints against the use of nuclear weapons. This disagreement of views leads to a puzzling question: in the absence of timely and reliable information, how do different security experts estimate the probability of such a nuclear attack by terrorist groups and how do they reach radically divergent conclusions? Political scientists, historians, academics, psychologists, and policy analysts have investigated several aspects of nuclear terrorism such as terrorist strategies and government response to any such act. The risk of a nuclear terrorist attack is defined as a product of the probability of such an attack times its consequences. However, the source of uncertainty in determining the level of the risk of nuclear terrorism is the lack of a clear assessment of motives and capabilities of terrorist groups. Without access to classified information, we cannot measure the capabilities and motivations of terrorist groups. The experts face similar challenges to assessing the risk of terrorists acquiring a nuclear bomb. These include lack of source material, the difficulty of considering all possible failure scenarios, and, most importantly, the fact that risk assessments are generally subjective. What makes it further problematic is that significant quantities of HEU and plutonium are frequently on the move not only between nuclear facilities in different parts of the country but also across national borders. This makes the achievement of a gold security standard for nuclear materials across the globe a more daunting task. The overall unavailability of quantifiable information, along with innumerable uncertainties and complexities has limited the discussion to normative interpretations reflecting the intellectual thought processes of these experts. In my view, this divergence of views is because different experts have been making different assumptions about the intentions and capabilities of terrorist groups. There are various ways in which experts have framed the debate over the probability of an act of nuclear terrorism. In the US, much of the literature revolves around the ‘key variables’ affecting the strategic-level decision-making process of terrorist groups. Because the literature has evolved largely in a Western security context, with little or no social variation, it tends to focus only on terrorism threats to Western societies. Specifically, two distinct assumptions dominate the nuclear terrorism literature. The first, articulated by scholars such as Matthew Bunn and Graham Allison, argues that terrorists are ideologically driven. In their view, the probability of nuclear terrorism is very high because such an attack is consistent with Al-Qaeda’s ideology. This school of thought assumes ideological considerations to be more important than political ones. These experts believe that for terrorists, as long as they are pursuing their ‘crazy’ objectives like global domination or killing non-Muslims, their every action can be justified as means to a divine end. Terrorist groups have largely religious-oriented and millenarian objectives and they tend to see their fight as a precursor to the Day of Judgement, thus considering mass casualties part of their agenda. In this context, the objectives of terrorist organisations are entirely detached from social constraints or any moral objectives. This set of assumptions leads to the view that terrorists are more likely to acquire nuclear weapons as it will not help them in acquiring a global status but also cause a wide-scale catastrophe. The second, articulated by scholars such as Jenkins and Kamp, argues that terrorists are resource driven. This school of thought believes nuclear terrorism to be a very remote and highly exaggerated threat. Terrorists are resource driven, and their use of violence is strategic and not indiscriminate. This framing allows very little scope for large-scale destruction because terrorists want more people watching than dying. This is so because terrorist organisations always need financial support to operate and they have their political constituencies, which would not allow indiscriminate killings of hundreds of thousands of non-combatants. The choice of assumptions has important consequences on scholars’ conclusions about the desire to acquire and/or use nuclear weapons. The reason is that ideological terrorists are likely to behave quite different than resource-driven terrorists. And the diverse assumptions these experts are making can be a function of their professional and career background. Experts like Graham Allison and Matthew Bunn have remained associated with successive US governments at different points in their career, and thus, they rate the possibility of nuclear terrorism as very high. Thus, it can be reasonably argued that experts interpreting the goals of terrorist organisations as driven by ideological beliefs have either access to more classified information due to their association with successive US administrations or tend to rate the possibility of nuclear attack high under some kind of political pressure. This shows that when experts argue on nuclear terrorism, they often talk past each other because they use different theoretical frameworks to assess the motives of terrorist groups. Nuclear terrorism is a real threat, and even a single act of nuclear terrorism would have unimaginably horrendous consequences for the global security. However, potential uncertainties and misconceptions exist because different aspects of nuclear events have not been consistently distinguished. With divergent paths to acquire certain capabilities and dozens of terrorist organisations, assessing the likelihood of nuclear terrorism would remain an uphill task. The writer is a US-based nuclear security analyst and can be reached at rizwanasghar5@unm.edu