Climatic change has been the subject of investigation and spirited debate for more than three centuries. One important element of this debate has been the search for and definition of unique, impermanent climatic regimes measurable by historic time. The Medieval Warm Period and the Little Ice Age are the two most commonly referenced and discussed of such regimes. This thesis examines the theories and debates that preceded and surrounded the formal definition of the Little Ice Age as an historic period of approximately 1550-1850 AD. This thesis begins by describing early attempts to measure and record climatic conditions during the late seventeenth and early eighteenth centuries while also demonstrating that climatic change and climatic influence were matters of concern for both the scientific and philosophical elite and the public. By the first decade of the nineteenth century, however, discussion of climatic change had begun to center on comparisons of the medieval past and the cooler present. Climatic change itself often intruded on debates about past climates during the early nineteenth century. By 1900, however, both scholars and laymen had begun to recognize that some form of climatic change had occurred in the sixteenth century. Early twentieth century scholars such as Otto Pettersson, Charles Rabot, and Ellsworth Huntington helped define the boundaries and significance of historical climatic regimes. When Francois Matthes wrote of a "little ice-age" in 1939, he was not creating a wholly new idea; he was instead engaging in a centuries-old debate over the climatic conditions of the last millennium.