This dissertation explores certain philosophical questions that arise around ‘marginal’ cases of disability, or cases that fall outside the paradigm of what disability is generally thought to be like. Throughout these three chapters, I hope to motivate that we have good reasons to pay closer attention to the ethical significance of conditions that seem, in various ways, to fall between the categories of disability and non-disability. Chapter 1 focuses on certain challenges to planning that arise from conditions that involve fluctuating symptoms. I suggest such cases can lead to a form of planning-agency that has not been discussed in the literature on action theory. Chapter 2 explores two dilemmas for the role that vagueness ought to play in theories of disability. I argue that we have reasons to reduce vagueness in our understanding of disability, and reasons not to reduce vagueness. I further argue that there are reasons to expand the category, and reasons to narrow its scope. Chapter 3 defends the merits of giving normative conceptions of disability, and proposes a novel normative account on which to be disabled is to have rights in virtue of being impaired. On the view that I defend, settling who is disabled is essentially an ethical question. I hope this dissertation moves theorists towards understanding debates about the nature of disability as necessarily involving ethical claims, and so not a project that can be done purely in the realm of descriptive metaphysics.