This chapter seeks to reorient how the political rationalities of imperial forms have been conceived. It considers how a focus on the “supremacy of reason” as the master trope of colonial government by which empire’s agents claimed their authority has displaced the affective work that such rationalities perform. It argues that such assumptions are not only unfounded; they occlude what constituted the practices of rule: the affective attachments encouraged, the sensibilities schooled, and the dark anticipatory fears engendered among those charged with colonial “defense.” The focus on reason displaces a crucial imperial genealogy and history of the present that forms the basis of contemporary imperial counterinsurgency, surveillance, security, and “preparedness” strategies. Here the concept work is around the sentiments and sensibilities that notions of security produce, on the subjects they endeavor to create, on the manipulations of space they condone, and on the objects of fear they nourish and reproduce.