 Values, such as liberty and equality, are sometimes said to be incommensurable in the sense that their value cannot be reduced to a common measure. And options, such as studying to become a lawyer or studying to become a philosopher, are sometimes said to be incomparable in the sense that neither option seems to be at least as good as the other. These possibilities are thought to raise deep questions about practical reason and rational choice as well as related questions concerning topics as diverse as akrasia, moral dilemmas, the plausibility of utilitarianism, and the foundations of liberalism. This entry outlines answers in the contemporary literature to these questions, starting with questions about the nature and possibility of these phenomena.