The U.S. Food and Drug Administration (FDA) regulates products accounting for 20% of U.S. consumer spending. Many of its actions depend on assumptions about behavior. Will people heed food recall notices? Will they follow medication schedules? Will they have realistic expectations regarding the benefits and risks of new products? Over time, FDA has increasingly made psychology integral to its processes for answering such questions. That progress has come when windows of opportunity have found psychologists with science relevant to FDA’s needs, FDA with staff who can translate that research into agency terms, and a regulatory arena that can accommodate behavioral evidence. These experiences suggest opportunities and obstacles for psychologists hoping to apply their science to the public good.