Why do we need to divide time into periods, and how do these divisions of time contribute to or impede our understanding? Unlike other studies of periodization that limit discussions to whether particular period definitions are true and accurate, Periodization: Cutting Up the Past delves into our wariness of such categorizing and the impulse to categorize historical time in the first place. This special issue of MLQ covers examples of periodization from the early modern to the present, including a range from the individual year to the longue duree and incorporates a variety of methods from close empirical study to global concern. In the lead essay, Russell A. Berman argues that periodization saves us from the dangers of both anachronism and presentism. Srinivas Aravamudan, updating Vico, reminds us that we lose the past if we simply leave it unexamined. In Perioddity, Timothy J. Reiss reflects on the crossings of chronology with geology in long-range and global perspectives. This collection strives to turn discomfort with periodization into a constructive discourse. Periods are presented as a challenge and an opportunity, a resource and a corrective.