This dissertation is a collection of essays under the theme of moral responsibility 'at the margins'. I investigate a number of examples of disordered agency and cognition -- self-deception, delusion, and addiction -- through the lens of a so-called `reasons-responsiveness' theory of morally responsible agency, employing the theory to examine the extent to which agents in those conditions are morally responsible, and in virtue of what this is so. In Chapter 2, after a brief introductory chapter, and before getting into the individual disordered phenomena, I develop and defend the reasons-responsiveness theory of responsible agency to which I will appeal in later chapters. Such theories -- according to which responsible agency is based in an agent's capacity for recognizing and responding to reasons for action -- are not entirely new. However, developed in the right way, they are also well-equipped to respond to a kind of skeptical challenge to morally responsible agency that has somewhat recently come into vogue. This skeptical challenge is motivated by recent findings in social and cognitive psychology that seem to show that much of human behaviour is motivated by considerations which are, from the perspective of justifying action, irrelevant. For example, contributions to a communal office coffee fund can as much as triple when the instructions are accompanied with a pair of watchful 'eyes'. I argue that of all mainstream theories of agency, the reasons-responsiveness theory is least threatened by results such as these. I further respond by addressing a dispute between reasons-responsiveness theorists themselves: what is required for someone to count as responding to reason? I argue for a liberal interpretation of this requirement on independent grounds, and note that such a version of the theory is even better equipped to respond to the skeptic, yielding a theory of agency which is actually enhanced by appeal to the empirical results. In Chapters 3 and 4 I develop a novel account of self-deception and use that account to address the question: Are some delusional subjects responsible for their delusions? The central difficulty for the philosophical theory of self-deception has been to yield a psychologically plausible description of its dynamics. Self-deception is also paradigmatically intentional behaviour for which agents are typically blameworthy. I argue that no extant account of self-deception can capture both of these features. On my account, what makes a state a self-deceptive one is not determined by how it comes about. Rather, it is determined by how that belief is maintained. Self-deception, on this view, is willful failure, a refusal, to meet epistemic requirements for motivationally biased reasons. Thus, self-deceivers are typically responsible for their self-deception. I further argue that if this account is correct, there will be at least some cases of delusion (e.g., the Reverse Othello and Capgras delusions) for which agents are, in some sense, responsible. Appealing to the distinction between blameworthiness and (what I shall call) 'attributability', I claim that this leads us not to the conclusion that delusional subjects should be blamed, but instead to a more nuanced understanding of the kind of agency involved in the dynamics of delusion, and of the reasons these subjects are excused. The final chapter is about addiction. Perhaps the central question raised by addiction is: to what extent are addicts responsible agents? Theorists notoriously oscillate between two extreme positions: (1) that addicts are just like unimpaired agents and are fully responsible and (2) that addicts helplessly suffer a condition that leaves them utterly without self-control. I argue against both extreme positions, engaging with current science at both turns. Against (2), I argue that there is no satisfactory understanding of the 'brain disease theory' of addiction that entails that addicts are not responsible agents. I then argue against (1) by considering addicts at different stages of addiction -- those who are aware of their predicament vs. those who are not (although they should be). With respect to the unaware, I argue that they share some features with the self-deceived which explains their insensitivity to a rationally circumscribed body of evidence. Concerning the aware, I appeal to empirical work on `ego-depletion' and willpower -- and to Chapter 2's theory of responsibility -- to argue that these addicts suffer a graded impairment of the will, one that partially excuses them from blameworthiness.