The reader of Philo's sprawling corpus encounters numerous non-biblical citations and allusions, but it is often difficult to achieve an overall sense of the differentiated significance of various authors and texts for Philo. In this paper, I hope to provide a broad, synthetic approach to Philo’s use of non-biblical sources. By taking into account the nature and number of his allusions to predecessor texts, and in particular by noting the distribution of his explicit quotations, the paper attempts to identify the shape of Philo’s debt to both literary and philosophical texts. An attempt will be made to relate the results to Greco-Roman education in Egypt, together with the question of which of his sources should be conceived of as full works, and which as doxographical or other collections.