Some of the most challenging questions in philosophical ethics concern the justification of action. Can you have reasons to do something that you are not, and perhaps cannot be, motivated to do? If reasons rest on desires, why respect the rights and interests of others when doing so prevents us from getting what we want? In other words, why be moral? In his 1979 essay, "Internal and External Reasons," Bernard Williams framed the dispute about reason and motivation in a way that captured the philosophical imagination. An explosion of work on reasons and action followed, with influential responses by Christine Korsgaard, John McDowell, and Michael Smith. This volume collects the most important work on the topic, including Williams's seminal essay, the responses by Korsgaard, McDowell, and Smith, and more recent contributions by central figures. Taken together, the selections offer a comprehensive survey of state-of-the-art work on internal reasons and a distinctive, focused approach to foundational questions of ethical objectivity. A substantive introduction by Kieran Setiya skillfully guides the reader through the theoretical and conceptual terrain, explaining what is at stake in the larger debate.