Political science, striving to uncover the regularities of political life, has paid scarce attention to its contingencies. This chapter takes up this task of clarifying the conceptual structure of contingency. After discussing some scholarly intuitions, ordinary uses, and lexical definitions of contingency, it extends a worrisome initial diagnosis. Contingency, it claims, suffers from a double conceptual liability: It is indeterminate in its empirical referents and unclear in its semantic structure. To resolve the semantic problem of meaning, much of this chapter addresses the empirical problem of reference. It draws a roadmap through multiple locations of contingency: individual actors and actions, conceptual, normative, and practical commitments, objective and subjective facts, causal relations, catastrophic and ordinary events. Mapping the multiple referents and uses of contingency leads the author to conceptualize contingency as a three-dimensional concept that involves indeterminacy (possible worlds), conditionality (causal justifications), and uncertainty (open futures).