Iamblichus, whose life spanned the late third and early fourth centuries, was one of the most revered Platonist philosophers. The Emperor Julian, who ranked him with Plato, planned to use his work as the philosophical basis for a revival of pagan religion to meet the Christian challenge. Iamblichus wrote On the Pythagorean Life as the first of ten volumes on the philosophy of Pythagoras. It is the most extensive surviving source on Pythagoreanism, and has wider interest as an account of the religious aspirations of late antiquity. The introduction and commentary aim to set On the Pythagorean Life in its double context of Pythagorean tradition and pagan-Christian debate, and to interpret historical allusions and Pythagorean and Platonist teaching.