The collection presented in this Special Issue has an interesting history. It began in 2008 when the Smith Richardson Foundation was pleased to receive an unusual number of grant applications across several disciplines to carry out randomized controlled trials. Although many of the applicants were eminent in their fields, most had little or no prior experience in the conduct of experiments.

Lawrence Sherman, as a Governor of the Smith Richardson Foundation, was keen to assist by introducing the successful grantees to colleagues who could advise about managing field experiments. With this in mind, in January 2009 he invited them to a two-day Workshop at the University of Pennsylvania where several experienced experimentalists from various disciplines discussed with them the research designs of their studies.

The papers of most of the Smith Richardson grantees who attended the Penn Workshop form the backbone of this Special Issue. Additional papers from other experimentalists relate their own troubles and triumphs conducting trials in criminal justice. Many of the contributors met again at the American Society of Criminology conference in November 2009 to compare notes and report progress in their presentations, and again at the annual Jerry Lee Crime Prevention Symposium at the University of Maryland in May 2011. On each occasion, they were able to discuss the headway they had made with their experiments and to reflect on their successes and regrets.

In these papers, the original contributors make thoughtful commentaries on what they have learned about conducting experiments, while the older hands consider their own extensive experience. All agree that the value of their research far outweighs the difficulties of the endeavour, and join enthusiastically in furthering the use of experimental research for answering vital questions in criminal justice.