The doctrine of the margin of appreciation that the European Court of Human Rights has developed in its case law has given rise to considerable criticism. In this article I draw a distinction between two different ways in which the Court has used the doctrine. The first one is in cases where the Court has to decide whether a particular interference with a Convention freedom is justified. In answering that question, the Court often uses the label ‘margin of appreciation’ without (...) drawing on a substantive theory of rights that can justify the conclusion reached. The second use appears in cases where the Court refrains explicitly from employing a substantive test of human rights review on the basis that there is no consensus among Contracting States on the legal issue before it. My aim is to highlight the principles that can be used to justify each use of the doctrine, by locating human rights within broader issues in moral and political philosophy. Particular emphasis is placed on the distinction between reason-blocking and interest-based theories of rights as well as on the nature of the duties of the European Court, as a matter of international human rights law. (shrink)