Jews have often been described as the moneylenders for medieval Europe and considered central in Europe's shift from a barter economy to a profit economy. By providing credit, the classic narrative holds, Jews performed a vital "economic function" when restrictions on "usury" prevented Christians from lending. This dissertation challenges that narrative historiographically and empirically. The classic narrative, I argue, was constructed in response to nineteenth-century debates over the emancipation of German Jewry (Chapter 2). It rests on two outdated theories developed by the German Historical School: a theory of economic stages and an organic model of folk development. Werner Sombart and Max Weber appropriated and transformed the narrative, and it persisted, against mounting evidence, in twentieth-century historiography. The scholarship on commercialization and the Commercial Revolution came to undercut the theoretical basis for the "economic function" ascribed to medieval Jewry. This literature in fact described commercialization without reference to Jews at all. But the implications for the narrative in Jewish history have not been drawn. I argue that empirical evidence shows that most Jews were not professional moneylenders (Chapter 3). In thirteenth-century England---which purportedly provides the strongest case for the classic narrative---most Jews belonged to an urban lower class, which scraped together a living from various occupations ranging from day laboring to huckstering and peddling. Jewish economic history, I argue, ought to envision Jews as Europeans undergoing commercialization together with Christians, rather than as an exterior, causal agent for commercialization. The commenda contracts of Jewish merchants from Marseille, involved in long-distance sea trade, suggest as much (Chapter 4). But even the literature on commercialization and the Commercial Revolution remains beholden to obsolete paradigms: It critiques the theory of economic stages but, in subscribing to the "rise of the money economy," remains rooted in it (Chapter 5). As a step toward rethinking the causal role attributed to money in the literature on the Commercial Revolution, I explore the meaning of money in the medieval mentalité (Chapter 6). Money, I argue, was not seen as a symbol of a new profit economy, but acted like a classic gift.