The collective ideologies of the 20th and 21st century have illustrated the horrifying scale of human atrocities that can be committed in the name of ideological groups and causes. While philosophers and historians have developed rich accounts of the societal factors shaping the forces behind participation in collective ideologies, there has been remarkably little rigorous scientific investigation into the cognitive and neural factors that can increase an individual’s susceptibility to ideological dogmatism and extremism. The aim of the current doctoral research was therefore to examine what psychological traits make some individuals more vulnerable to ideological thinking than others. Theory-driven and data-driven approaches were employed to map out the cognitive underpinnings of ideological thinking. A series of large online studies encompassing over 1,500 participants revealed that ideological rigidity may be rooted in cognitive rigidity, such that the rigidity with which individuals process and evaluate neutral stimuli predicts the rigidity and extremity of their ideological beliefs. This relationship was corroborated across multiple ideological domains, including nationalism, religion, political partisanship, dogmatism, and extremist attitudes, uncovering a tight link between low-level perceptual processes and high-level ideological attitudes. Furthermore, a data-driven approach using Bayesian analyses was adopted to study the cognitive and personality signatures of political conservatism, nationalism, religiosity, and dogmatism. This exposed that psychological dispositions can predict ideological attitudes substantially better than traditional demographic variables, challenging the dominant perspective in the social sciences that socioeconomic indicators are the most powerful predictors of how citizens vote and what they believe. This research program therefore suggests that ideological attitudes are amenable to careful cognitive and computational analysis. The findings signify that individual differences in our cognitive dispositions may underpin the intensity of our ideological adherence – and so a rigorous scientific study of the ideological mind may illuminate pertinent societal questions facing modern democracies.