Sexual Issues played a significant role in Judaism’s engagement with its Greco-Roman world. This paper will examine that engagement in the Hellenistic Greco-Roman era to the end of the first century CE. In part sexual issues were a key element of demarcation between Jews and the wider community, alongside such matters as circumcision, food laws, sabbath keeping and idolatry. Jewish writers, such as Philo of Alexandria, make much of the alleged sexual profligacy of their Gentile contemporaries, not least in association with wild drunken parties, same-sex relations and pederasty. Jews, including the emerging Christian movement, claimed the moral high ground. In part, however, matters of sexuality were also areas where intercultural influence is evident, such as in the shift in Jewish tradition from polygyny to monogyny, but also in the way Jewish and Christian writers adapted the suspicion and sometimes rejection of passions characteristic of some popular philosophies of their day, seeing them as allies in their moral crusade.