Under the influence of Hellenistic culture and politics, the Hasmoneans re-fashioned the Judaean state into a league that would allow the incorporation of non-Judaeans. At more or less the same time, the progression from ethnicity to religion had advanced to the point that individual gentiles who came to believe in the God of the Jews were accepted as Jews themselves. But these two models of "conversion, " political enfranchisement and religious change, were not the only ways in which a gentile could cross the boundary and become a Jew. The boundary was fluid and not well marked, and there were competing definitions of it.

According to rabbinic law, the status of the offspring of intermarriage is determined matrilineally: a Jewish mother bears a Jewish child, a non-Jewish mother bears a non-Jewish child. Shaye J.D. Cohen discusses the contexts in which the prohibition against intermarriage evolved, and makes somefresh suggestions about what influenced its evolution. A final section studies a Mishnaic text that stands at the intersection of several of the book's concerns: matrilineal descent, conversion, and the tension between Jewishness as ethnicity and Jewishness as religion.