Abstract: The Athenian democracy developed striking institutions that, taken together and separately, have long engaged the attention of theorists in law, politics, and history. We will offer a unifying account of the major institutions of the Athenian constitutional order, attempting both to put them in their best light and to provide criteria for evaluating their successes and failures. Our account is that Athenian institutions are best understood as an illustration of precautionary constitutionalism: roughly, the idea that institutions should be designed to safeguard against political risks, limiting the downside and barring worst-case political scenarios, even at the price of limiting the upside potential of the constitutional order. We use this framework to illuminate some of the distinctive features of the Athenian democracy: selection of officials by lot, rotation of office, collegiality, ostracism, and the graphe paranomon (the procedure for overturning an unconstitutional decree). Under some circumstances, precautionary constitutionalism is a useful strategy of institutional design. Under other circumstances, however, precautionary constitutionalism can go wrong in characteristic ways – by perversely exacerbating the very risks it seeks to prevent, by jeopardizing other values and thereby imposing excessive costs, or simply by creating futile precautions that fail the test of incentive-compatibility. We evaluate the precautionary institutions of the Athenian democracy in this light, and suggest that some failed while others succeeded. While selection by lot, rotation, and collegiality proved to be enduring and incentive-compatible institutions, ostracism perversely exacerbated the risks of tyranny and political domination it was intended to prevent, and the graphe paronomon collapsed into futility.