Motivational internalism-the idea that there is an intrinsic or necessary connection between moral judgment and moral motivation-is a central thesis in a number of metaethical debates. In conjunction with a Humean picture of motivation, it provides a challenge for cognitivist theories that take moral judgments to concern objective aspects of reality. Versions of internalism have potential implications for moral absolutism, realism, non-naturalism, and rationalism. Being a constraint on more detailed conceptions of moral motivation and moral judgment, it is also directly relevant to wider issues in moral psychology. But internalism is a controversial thesis, and the apparent possibility of amoralists and the rejection of strong forms of internalism have also been seen as problems for non-cognitivists.This volume's thirteen new essays and introduction are meant to help readers appreciate state-of-the-art of research on internalism, to identify connections between various aspects of the debate, and to deepen discussion of a number of central aspects of metaethics. The introductory chapter provides a structured overview of the debate with a focus on the last two decades, while the book's three main sections focus on what evidence there is for or against various versions of internalism, the relevance of versions of internalism for wider metaethical issues, and different ways of accommodating both internalist and externalist aspects of moral practice, respectively.