Advocacy by psychologists has often been portrayed as requiring immersion in the processes of public policy. In the area of intellectual disability, many relevant laws have been passed, court cases fought, and administrative decisions made. These policy decisions have, however, sometimes been based on a division of labor, with psychologists doing the research and lawyers and representatives of parents' groups carrying out most of the advocacy. It now appears that some of the earlier advocacy by psychologists in this area had unfortunate results. This is partly because some of it was based on flawed research and partly because our values have changed over time. Some more recent instances of advocacy, better grounded scientifically, had more favorable effects. Nevertheless, there is clearly not a simple linear relation between research findings and policy. Ample illustrations of these statements are provided in the careers of four psychologists who were influential as advocates in this domain during their lifetimes: Henry Goddard, Cyril Burt, Jack Tizard, and Donald M. Baer.