Problem-solving courts differ from traditional criminal courts because they are designed to treat the underlying problems that lead to criminal conduct. These courts originated in the late 1980s with a focus on drug offenders and have since expanded to other groups such as veterans. As an alternative way to deliver justice, problem-solving courts have been through much experimentation and refinement in their 30-year history. This article, which is part of a special issue of the NIJ Journal commemorating the Institute's 50th anniversary, traces NIJ's central role in researching and evaluating different models for problem-solving courts. It highlights several NIJ studies of the courts' effectiveness, including an ongoing study of veterans treatment courts that is part of the U.S. Department of Justice's coordinated response to the opioid crisis.