This collection of papers presents a representative selection of NIJ's portfolio of gang-related research. The genesis was the upsurge in gang crime beginning in the mid-1980s, which prompted NIJ to expand research in this area. NIJ's major focus is to generate research-based knowledge that can inform policy and be useful for practitioners. For that reason, the emphasis in this volume is on evaluations. An evaluation may indicate a program works or doesn't, but in either case the information can be applied by those seeking solutions to similar problems.