To describe a unified Jewish identity in the Mediterranean in the period between 200 BCE and 200 CE is incorrect, since each Jewish community approached its identity in unique ways. These varied on the basis of time, place, and how the non-Jewish population reacted to the Jews and interpreted Judaism. This thesis examines the three major centres of Jewish life in the ancient world - Rome, Alexandria in Egypt, and Judaea - demonstrate that Jewish identity was remarkably and surprisingly fluid. By examining the available Jewish, Roman, and Greek literary and archaeological sources, one can learn how Jewish identity evolved in the Greco-Roman world. The Jews interacted with non-Jews daily, and adapted their neighbours’ practices while retaining what they considered a distinctive Jewish identity.