In this doctoral thesis, I address questions concerning teleology, chance, and necessity in Aristotle's philosophy. These three concepts are closely related. Aristotle considers chance in relation to teleology, and contrasts his conception of teleology with his own and his predecessors' views of necessity. He explains accidental causation on the basis of the absurdity of necessitarianism. In Chapter I, I clarify Aristotle's definitions of chance events and chance in Physics B 4-6 on the basis of a detailed examination of 'coming to be accidentally' (196b23), 'for the sake of something' (196b21), 'might be done by thought or by nature' (196b22). I analyze accidental and non-accidental relations involved in the marketplace example. In Chapter II, I argue that Aristotle accepts that the regularly beneficial winter rainfall is for the sake of the crops in Physics B 8. I scrutinize Empedocles’ view as described by Aristotle and show that it is not a theory of natural selection. I seek to show that the rival view against which Aristotle argues is an amalgam of reductionism and eliminativism. In Chapter III, I analyze what Aristotle means by 'simple necessity' and 'necessity on a hypothesis' (199b34-35), and argue that, in Physics B 9, he only acknowledges hypothetical necessity. Scrutinizing the wall example and Aristotle’s reply to it, I clarify his view of the relation between teleological causation and material necessity. In Chapter IV, I clarify Aristotle's conception of accidental causes, while taking his presentation of the necessitarian argument in Metaphysics E 3 as a reductio ad absurdum. I criticize the view that Aristotle himself accepts necessitation in this chapter. In doing so, I argue that, although this point is not explicitly stated in Physics B, Aristotle thinks that what is accidental is not necessary prior to its occurrence.