In United States v. Leon, the Court ruled that the exclusionary rule need not be applied to remedy fourth amendment violations when the evidence was obtained by law enforcement officers who were acting in reasonable, good-faith reliance on a search warrant later found to be defective in certain respects. This study focused on the decision's impact on policies and practices of police, courts, and prosecutors. It also examined related State court rulings and responses of law enforcement administrators. Data came from 37 locations, through reviews of applications for search warrants, interviews with criminal justice personnel, and analyses of recent State supreme court decisions. The decision has not changed the process used, the quality or quantity of search warrants, or judicial suppression of evidence. Patrol officers have little awareness of the Leon decision; other police personnel have varying knowledge depending on their rank and involvement in search warrant practices. The highest courts of eight States appear to have adopted the exception found in the Leon decision. Two State courts have rejected it. Nine have expressly declined to decide the issue, and the others have not heard cases involving the issue. Police and prosecutors have not made administrative changes in the search warrant process. As States resolve the questions surrounding the definition of good faith and its applicability to search warrant procedures, a more substantial impact may occur in the future. Tables, figures, and appendixes presenting study instruments and background information.