As part of a larger exposition on the Ten Commandments, Philo offers in Spec.4.78b-131 a detailed exposition of both the Tenth Commandment, which he reads simply as You shall not desire, and the Mosaic dietary laws, which he identifies as a distinct set of subsidiary laws designed to promote observance of the Tenth Commandment. Setting his exposition in the context of Middle-Platonic moral psychology, this dissertation answers two fundamental questions: First, what, in Philo's view, does the Tenth Commandment prohibit? (All desire? A certain type? What type?) Second, how, in Philo's view, is the Tenth Commandment observed? (What are the mechanics of its observance? What role do the dietary laws play in its observance?)