In discussing the need for experiments in criminal justice settings, this article provides three examples of what is apparently a much larger public and professional interest in better evidence about which interventions work. The new international Campbell Collaboration has been created to prepare and maintain systematic reviews of randomized experiments (and high-quality quasi-experiments) on interventions in crime and justice, education, social work, and social welfare. Almost simultaneously, although independent of the Campbell Collaboration, the American Society of Criminology, one of two professional associations representing criminologists nationally, went on record in support of an experiment that tested the effectiveness of a specific government-mandated intervention for convicted offenders. Further, this year marked the formation of the Academy of Experimental Criminology (AEC). Fellowship in the AEC is given to those researchers who significantly add to the pool of knowledge by conducting experiments in the criminal justice field. These examples evidence a much larger public and professional interest in better evidence about which interventions work. This interest is reflected in contemporary conferences, law, research practice, and the regular use of rhetorical phrases such as "evidence-based policy," "evidence-based education," and "what works."