This paper uses hysteresis to develop the concept of policy lock-in and lock-out. Policy changes may near-irrevocably change the economy’s structure, thereby changing the distribution of wealth, income and power. That may lock-in policy by changing the political equilibrium. Exit costs that block policy reversals also cause lock-in. Conventional thinking treats policy as a dial which is adjusted according to the economy’s state. Policy lock-in questions the dial formulation and raises new issues for optimal policy design. It also offers insights into economic and political crisis theory. Policy lock-in is illustrated with examples that include tax policy, government spending, the euro, globalization, and the neoliberal policy experiment.