The prevailing conceptions of constitutions ordinarily characterize them as rigid and long-enduring, if not permanent, documents. This Essay challenges that prevailing wisdom on both descriptive and normative grounds by providing the first systematic examination of temporary constitutions, exploring their benefits as well as their costs, and providing prescriptions for their optimal use. A temporary constitution or constitutional provision, as this Essay defines it, limits its own term and lapses at its expiration date unless reenacted through regular constitutional amendment procedures. Although underexplored and undertheorized, temporary constitutions have an extensive historical pedigree and neglected benefits for constitutionalism. Temporary constitutions can reduce error costs associated with entrenching a norm in a durable constitution and promote incrementalism and experimentation in constitutional design by allowing constitutional drafters to consider a greater quality and quantity of information about the empirical effects of their constitutional choices. The use of temporary constitutions can also reduce cognitive biases that tend to predominate in constitutional moments and promote consensus building among constitutional designers by lowering the decision costs involved in negotiating and reaching a constitutional bargain. Finally, temporary constitutionalism can respond to the central critique of durable constitutions by easing the dead hand problem, which refers to the ability of the constitutional founders to entrench norms that bind future generations. Temporary constitutions, however, can also impose their own costs on the polity by undermining constitutional stability and design efficiency, and by injecting different types of cognitive biases into the design process. This Essay analyzes these costs, offers some prescriptions for minimizing them, and studies the advantages and disadvantages of temporary constitutions vis-à-vis other strategies of constitutional design intended to ease constitutional rigidity or permanence, including by law clauses, low amendment thresholds, and constitutional vagueness.