This chapter will consider radicalisation from the perspective of George Kelly's (1955/1991) personal construct theory. The theory asserts that people are primarily concerned with anticipating their worlds, which they do by developing hierarchically organised systems of personal constructs. Difficulty in anticipating the world is associated with feelings of anxiety and alienation. Radicalisation is more likely in individuals who have difficulty in predicting their worlds, perhaps because their construing is inconsistent with a culture's shared meanings, and/or have a less stable self-construction. Radicalisation is associated with an extreme negative construction of a hated group. The construction of the hated group provides radicalised individuals with a construct system that offers greater structure and predictive power and, therefore, provides more meaning to life than would exist if this construction were absent.