In scores of passages across his extensive corpus of writings, Philo of Alexandria takes care to distinguish between voluntary and involuntary sin. While various subsequent interpreters have recognized Philo's interest in this matter in general terms, no focused and extended study of the phenomenon has been offered previously. What motivates Philo's fascination with this issue, and what are the primary influences on Philonic thought with regard to this distinction? To what degree does Philo discover a similar concern in scripture, and how does Philo's reading of particular texts compare with that offered by other early interpreters of scripture? These are the kinds of questions explored in the present dissertation as it offers a preliminary account of Philo's conceptualization of the distinction between voluntary and involuntary sin. The dissertation evaluates the ways in which Philo's attention to the distinction between voluntary and involuntary sin represents an unsurprising emphasis for this exegete of scripture. As a reader of the Greek Bible, Philo sometimes finds in the texts he interprets a roughly similar concern, and that, on occasion, utilizing the terminology that dominates Philo's vocabulary for the voluntary and the involuntary. Correspondingly, the identification of different sins according to an agent's volition, intention, or knowledge is a common phenomenon among other Second Temple authors.The dissertation demonstrates, nevertheless, that the primary influence on Philo's treatment of the distinction between voluntary and involuntary sin is the prominent and enduring concern with the distinction between voluntary and involuntary error or wrongdoing that emerges in a very wide range of classical and post-classical sources, and becomes a particular point of philosophical-ethical focus in regard to the distinction between the voluntary and the involuntary in the analysis of human agency and action. The dissertation argues that the strength and scope of Philo's interest in the distinction between voluntary and involuntary sin should be understood as a function of his assessment of the condition and responsibilities of created humanity, and the usefulness of the distinction as an index to the ethical standing of different kinds of soul. The peculiar privilege of created humankind is possession of the rational mind, gifted with freedom from necessity, or the voluntary faculties. Voluntary sin is, then, by its nature a very serious thing, a denial of the creator's claim on the creature and the mark of a thoroughly reprehensible soul. In contrast, involuntary sin is simply an unfortunate entailment of created human existence, an inevitability of life in the corporeal realm for those who cannot escape the non-rational within and without, even exemplary souls still in the process of striving for virtue.