This chapter construes positive freedom as an ideal of individual self-mastery.So understood, positive freedom concerns internal factors that, in Isaiah Berlin’s words, “determine someone to do, or be, this rather than that?”Self-mastery is a matter of being determined in the right ways by these internal factors.This chapter first explains how self-mastery contributes to the quality of the lives of those who achieve it.It does so in different, but complementary ways, ways which have not been distinguished or adequately appreciated in the literature on the topic.The chapter next argues that self-mastery is one component of the kind of freedom that a well-functioning state ought to promote in its members.Self-mastery is an individual achievement, but the state can promote it by establishing conditions that facilitate its realization.In presenting these arguments, the chapter rejects the view – sometimes advanced by proponents of positive freedom – that the value of external negative freedom is reducible to its contribution to positive freedom, but it concurs with the view – often advanced by proponents of positive freedom – that the state’s concern with freedom should not be limited to external factors, such as constraining coercion or ensuring that all have access to an adequate range of options.