In numerous passages in his exegetical works, Philo displays a pronounced interest in the distinction between voluntary and involuntary sin. Sometimes the interest appears to arise quite readily from the subject matter of the scriptural text itself. In many cases, however, the text in question shows no evident concern with the intentions of the human agent, or even the idea or phenomenon of sin. The latter cases are, quite predictably, most prevalent in Philo’s allegorical exegesis, and emerge, in a variety of ways, in relation to Philo’s programmatic concern to interpret scripture allegorically as an account of the experiences and ethical progress of the individual human soul. What motivates Philo’s interest in the distinction between voluntary and involuntary sin as it emerges as a function of the allegory of the soul? This is the question addressed in this paper. We will proceed in two stages. First, we will consider the primary ways and issues in relation to which Philo’s concern with the distinction between voluntary and involuntary sin is evident in his allegorical account of the career of the soul. We will give particular attention to Philo’s understanding of the constitution and plight of created humanity, and the psychology of human action. We will also address the ways Philo maps the distinction between voluntary and involuntary sin onto a range of characters named in the pentateuchal narrative—and, so, relates it to a spectrum of dispositions of the individual soul. Second, we will consider the significance of these findings, and that in light of the primary scriptural and extrascriptural influences on Philo’s conceptualization of different kinds of wrongdoing, and so offer an explanatory account of Philo’s allegorical concern with the distinction between voluntary and involuntary sin.