An important part of the American Psychological Association’s (APA) mission is to advance psychological science “to promote health, education, and public welfare.” Organizations with powerful influence on human welfare include state and federal appellate courts, especially the U.S. Supreme Court. Initially, APA’s amicus briefs focused on issues of importance to both individual psychologists and public policy. As the program evolved, APA increasingly focused on informing the courts about psychological science relevant to important legal issues, including criminal, civil, juvenile, education, disability, and human rights law. These briefs, and the science that supported them, consistently challenged stereotypical beliefs of laypeople with solid, easily understood empirical research. APA impartially advocates for the use of psychological science research findings by the courts, not on behalf of parties. Volunteer experts, including representatives of relevant APA divisions, participate in creating APA briefs. On occasion, other scientific organizations may join with APA in its filings. The measure of an amicus brief is broader than citations in appellate decisions. Although APA’s briefs have been cited many times by courts, a broader impact of APA briefs is seen by references to psychosocial research provided by APA in decisions where its briefs were not specifically cited. APA briefs are being read and are affecting major legal decisions. For APA, the relevant question is not whether its briefs “prevailed” in a case but whether the court was able to render a more informed decision. An important benefit of APA’s amicus program has been advancing both the reputation of psychological science and APA.