NIJ is soliciting applications for research and evaluation projects that advance the understanding and practice of gang prevention, intervention, and enforcement. At the group level, gangs vary from small local "crews" that are active for only a short period, to multigenerational gangs with local subgroups across multiple states or nations. Gangs also vary widely in terms of organizational sophistication. Across these group-level variations, gang membership continues to be one of the strongest independent predictors of serious offending at the individual level. Given the ongoing challenges that gangs present to States and localities across the Nation, it is especially important to provide practical knowledge to support improved antigang efforts.