In this dissertation I will study the commercial networks created by Jewish merchant families in Warsaw between 1750 and 1815. I will argue against the long-prevailing narrative of a decline of Polish Jewry in the eighteenth century and demonstrate that Jews played a crucial role in the Polish economy as merchants and suppliers. Presumably Jews -contributed significantly to the transformation of the Polish economy towards industrialization. By exploring the commercial networks as well as the role of merchants as political and cultural agents, I want to go beyond the question that was posed by Max Weber and Werner Sombart nearly a century ago: Whether religion in general and Judaism in particular were crucial factors for the emergence of capitalism. This is an historical project that will rely upon archival material and library, collections in a number of archives in Germany, Poland, the Ukraine, Latvia, the Netherlands as well as archives in Israel. I will explore five different themes based on the example of a number of important merchant families in Warsaw. The first will consider the prosopography of Jewish family and commercial networks and explore their ties to the Polish king, Polish nobles and non-Jewish merchants. In the second theme, I will look at the political involvement of Jewish merchants in questions of Jewish reform and emancipation that emerged at the end of the eighteenth century. The third will be the influence of religious attitudes and observance of Jewish merchants on their commercial activities. In the fourth area I will examine the transfer of culture through merchants and trade. Finally, I will interpret the commercial activities of Jewish merchants in Poland in the light of the general economic development and the beginning of industrialization at the tum of the nineteenth century. In this way, my dissertation will not only make a contribution to Jewish history but also to general European economic and social history.