This thesis is an investigation into the nature of those abilities that are relevant to free will when the latter is understood as requiring the ability to do otherwise. I assume from the outset the traditional and intuitive picture that being able to do otherwise bestows a significant kind of control on an agent and I ask what kinds of ability are implicated in such control. In chapter 1 I assess the simple conditional analysis of the sense of 'can' relevant to free will, and I agree with the consensus that this analysis fails. In chapter 2 I consider Kadri Vihvelin's contemporary version of the conditional account, which is cast in terms of dispositions. I develop, via engagement with Vihvelin's view, an account of how modal properties such as dispositions and abilities should be individuated. In chapter 3 I use this account to show why Vihvelin's account of free will is unsatisfactory. I also show how it helps us to better understand a distinction that is often made in the free will literature, namely, that between some notion of 'general' ability on the one hand and a notion of 'specific' or 'particular' abilities on the other. I argue that there are two important distinctions, both of which are relevant to free will. In chapter 4 I consider Keith Lehrer's analysis of 'can' and conclude that while it fails to achieve Lehrer's stated aim - namely, that of demonstrating that free will is compatible with determinism - it does contain some useful insights about the kinds of ability relevant to free will. In the fifth and final chapter I switch gears somewhat; I argue that various conditions typically treated under the banner of 'the epistemic criteria on moral responsibility' should instead be treated as conditions on an agent's being able to do otherwise.