In Conversion, Miriam Bodian considers the now-universalized term "conversion" in a Jewish context as broadly as possible, as an act of socioreligious boundary crossing. It charts how, across the long arc of Jewish history from biblical times to the present, patterns of boundary crossing have developed and shifted, whether of Gentiles entering Jewish life or of Jews exiting from it. It analyzes the biblical passages that have informed Jewish thinking about what is required to become a Jew before turning to the early rabbis' institution of a ritualized process of conversion. It then considers the protean ways in which Gentiles have become Jews and Jews have joined other religious communities from medieval to modern times. A further section is devoted to the complexities of conversion in the contemporary Jewish world, where conversions are not necessarily recognized across denominations, where substantial intermarriage has eroded the traditional boundaries between Jew and Gentile, and where the modern state of Israel plays a role that reaches beyond its borders in determining who is a Jew.