Our professional practice of grouping cultural products into historical categories has recently been the subject of lively critical discussion, as well as some consternation. Here I want to consider how, and how well, periodization organizes knowledge in the field of comparative literature. Organizing knowledge is what scholars do in all disciplines, of course, but the organizational models differ according to our objects of study. Historians may be the most dependent on schemata of periodization, but literary scholars aren't far behind. Literature curricula in United States universities are largely organized according to diachronic historical categories, whether they are labeled by centuries or by rubrics tied to a historical period's style or ideology or political circumstances. This is not surprising since European periodic categories long precede the establishment of curricula in the United States. Periods are powerful because they carry with them their own historical accumulations and applications, and they become dialectical as we engage their diverse cultural and historical meanings. For this reason, they can be particularly useful to comparatists. Indeed, to speak of any period at all is to make a comparative statement. One period necessarily implies others, each period a part that exists in relation to other parts and to an implied whole—a provisional “classification of the universe,” to quote from the passage by Jorge Luis Borges that I take as my epigraph.