This paper examines the incomplete and endogenous take-up of unemployment insurance (UI) benefits and its implications on policy. Standard models of UI focus on how benefit generosity affects unemployment duration, assuming perfect take-up. Yet, receipt is not automatic with estimates of take-up of around 50 percent in the United States. We show take-up is an important margin of response: If benefits become more generous, more workers claim benefits in addition to claimants remaining on benefits for longer. Using a sample of likely eligible workers, we leverage a regression kink design to identify the causal effect of weekly benefit level on take-up and total benefit duration. Our results suggest a 10 percent increase in the benefit level leads to a 4.8 percent increase in take-up, which drives a 6.4 percent increase in total benefit duration. In designing policy, accounting for the take-up response increases the expected cost of raising benefit levels. As a result, the wedge between the optimal benefit level and full insurance doubles and the marginal value of raising benefit levels decreases by 22 percent.