I implement event study and difference-in-differences research designs to measure the causal effects of mandatory waiting periods for abortions, distinguishing between "one- trip" waiting periods that allow counseling and information to be provided remotely and "two-trip" waiting periods that require two in-person appointments. The results suggest that one-trip waiting periods do not have substantial effects on abortions or births. Two-trip waiting periods are estimated to reduce abortions and delay those that still occur, increasing second trimester abortions by 19.1%, reducing resident abortion rates by 8.9%, and increasing births by 1.5%. These effects are larger for young women and for women of color. These effects also are larger in counties that are far from abortion providers and in counties with high poverty and unemployment. These findings support a "burden" rather than a "cooling-off period" interpretation of the findings.