This dissertation examines the ways in which Jews in the Second Temple Period used the book of Genesis for legal purposes. While the book of Genesis is part of a larger corpus referred to by terms related to law (torah in Hebrew and nomos in Greek), Genesis poses a problem, as it contains relatively little legal material, and takes place prior to the formal giving of the law at Sinai. This dissertation looks at the ways in which Jews in the second temple period grappled with the place and role of Genesis in the Torah, as they relate to halakhah, and focuses on the following questions: What was the status of the Law prior to Sinai? Did the Patriarchs observe the Law,and why? What is the relationship between Genesis and Sinai? Was Genesis treated differently as a halakhic source than the other books of the Pentateuch? While previous studies have examined aspects of these questions, none have provided a comprehensive overview of the issues as they relate to second temple Judaism as a whole. The introduction places these questions in their historical and scholarly contexts. The second chapter focuses on the book of Jubilees. The third chapter examines the Qumran scrolls across various genres. The fourth chapter looks at passages within Philo and Josephus, which relate to Genesis and halakhah. The fifth chapter shifts to early Christian literature, and examines the Gospels and the Pauline letters. Based on an examination of all of these texts, it is clear that the relationship between Genesis and halakhah played an important role in the halakhah and theologies of second temple Jews. Some texts reflect an intentional incorporation of Genesis in halakhic contexts, while others avoid doing so. Additionally, there is a positive correlation between the use of Genesis for halakhah, and the question of whether the Patriarchs observed the law prior to Sinai.