This article presents some theoretical reflections, and one empirical case study, on the contribution of geopolitics to the study of EU foreign policy. The article asks in particular how geopolitics can contribute to causal explanation in foreign policy. First, the article identifies and discusses two problems with a crude, early version of geopolitics: arbitrariness in the measurement of dependent and independent variables, and spurious causation. Second, drawing from concepts developed by rational choice theorists, the article argues that geopolitics can prove insightful in at least two ways. The first way in which geopolitics can establish causal explanations is when it studies how geography provides opportunity to act, that is, options for a political actor. The second way in which geopolitics is useful is that it can establish causality through negation (an event was prevented, or made more difficult, by geographical features). Both ways are illustrated through the example of empires and colonialism and their influence over EU foreign policy.