The U.S. Department of Justice released the first national guide for collecting and preserving eyewitness evidence in October 1999. Scientific psychology played a large role in making a case for these procedural guidelines as well as in setting a scientific foundation for the guidelines, and eyewitness researchers directly participated in writing them. The authors describe how eyewitness researchers shaped understanding of eyewitness evidence issues over a long period of time through research and theory on system variables. Additional pressure for guidelines was applied by psychologists through expert testimony that focused on deficiencies in the procedures used to collect the eyewitness evidence. DNA exoneration cases were particularly important in leading U.S. Attorney General Janet Reno to notice the eyewitness literature in psychology and to order the National Institute of Justice to coordinate the development of national guidelines. The authors describe their experience as members of the working group, which included prosecutors, defense lawyers, and law enforcement officers from across the country.