Abstract: Increased interactions among peoples and states combined with the growth of written constitutions are creating new opportunities for “extra-territorial” forms of constitutional interpretation, that is, the interpretation of domestic constitutions by “outsiders.” This article considers the potential benefits, and dangers, of outsider interpretation. It also identifies factors relevant to the appropriateness or legitimacy of such practices, drawing from analogous rules and doctrines developed in the context of U.S. federalism and international law.