In this dissertation, I analyze a range of epistemological and religious arguments for and against the fear of comets, as articulated in pamphlets and polemics following the comets of 1680-82 in the Spanish and English Empires. These works appeared in England, Spain, North America, and the Viceroyalties of New Spain and Peru. Against recent scholarship, I argue that the religious and political diversity which drove the "vulgarization" of comets in England was less important in other regions than technical disputes over the foundations of astrology, or long-standing religious distinctions between licit and illicit interpretations of wonders. After an introduction, four thematic chapters explore responses to the comets of the 1680s in England, Spain, North America, and Spanish America respectively. In chapter two, I show how the politico-religious appropriation of the comet led to the association of comet-interpretation with vulgar segments of society. In subsequent chapters I show that the political prodigy-mongering found in England was, in the Spanish empire, controlled through censorship of the press and a Catholic tradition of strict separation between miracles and wonders. This shared intellectual tradition led the conversation of the comet to hinge on fairly technical aspects of natural philosophy and astrology, which constrained the possible meanings of the comet. Chapter Four shows that the same division between licit and illicit interpretation of comets operated in the Puritan context of New England. Chapter Five elaborates on the Catholic background established for Spain by showing how broad religious trends intersected with local circumstances of patronage and norms of argument in shaping the debate in Spanish America. Finally, the conclusion reflects on how the diversity of questions at stake in the last debate over the meaning of comets in the 1680s changes our understanding of the decline of prodigies, wonders, and superstition more generally.