This thesis develops a tectonic theory of moral responsibility. The word ‘tectonic’ is used metaphorically, to bring to mind the interaction of tectonic plates in the earth’s crust. The theory of moral responsibility developed in the thesis posits that there are two aspects of persons that should be considered within moral responsibility judgments: agency and patiency. I suggest that the ways that these relate to and influence each other can be thought of as similar to the interactions between tectonic plates. I use the term ‘agency’ in its usual sense to refer to the control component of moral responsibility judgments. A person must be an agent, i.e. have a normal degree of self-control in order to be held morally responsible for her actions. This is a vague take on agency, to be sure. However, the tectonic theory is meant to apply to any of the common conceptions of agency in the moral responsibility literature. The vagueness in my treatment of agency is thus intended to allow the tectonic theory to be pluralist in regards to various conceptions of agency on offer. Whether one subscribes to a reasons-responsiveness view of agency, or an identificationist view, the tectonic theory’s prescribed concern for patiency can function as a fairness-enhancing counterweight to the agentic considerations of either view. The novelty of the tectonic theory derives from its use of the concept of patiency, which has been neglected in philosophical discussions of moral responsibility. Patiency refers to the features of a person and her life that she cannot control. The tectonic theory takes both agentic and patientic features of persons into account when making moral responsibility judgments. I argue that doing so can enhance the fairness of moral responsibility judgments, while for the most part avoiding the pitfalls of more conventional approaches to moral responsibility such as compatibilism and incompatibilism. To develop the tectonic theory, I draw from work in philosophy, psychology, and cognitive neuroscience.