Why should we study philosophy? Is it too abstract or too remote from real life to be of any value? Aristotle's Defence of Philosophy in the Protrepticus examines Aristotle's response to such questions. Based on an examination of the fragments his Protrepticus, Ronja Hildebrandt argues that Aristotle defends philosophy--understood as knowledge of the fundamental causes of nature and of happiness--on the basis of both its utility and its intrinsic value. Philosophy is useful because it enables us to become authoritative judges of how to live well, equipping us to reconsider social conventions and chart our own courses. But it also has intrinsic value: doing philosophy is either identical with happiness or a part of it, as it is the human function (ergon) and end (telos). For this reason, Aristotle claims, only those who philosophize truly enjoy living a human life. Hildebrandt challenges the common view that the Protrepticus reflects an early, merely Platonic phase of Aristotle's thought, showing instead that it articulates positions that are consistent with, and often illuminate, central themes in other of his extant works. This book thus provides a deeper understanding of questions such as whether Aristotle's view of happiness is monistic or inclusive, how he would respond to common objections against his ergon or function arguments, how he justifies teleology in nature, what role practical wisdom plays in virtuous action, and how he conceives of degrees of goodness, being, and living.