The influx of "crack" cocaine led to the growth of the 1980's street gang culture in America's cities. Along with drug use, abuse, and trafficking came abundant firearms and escalating violence. Juvenile homicides and armed assaults spiraled as gang members became entrenched in a repetitive cycle of destruction. Against this background, probation officer Bill Stewart observed the failure of conventional probation practice to influence individual youths whose dangerous lifestyle promised death or long incarceration. In response, he helped establish Operation Night Light. It started as an experiment in 1993 and 1994 with two police officers and two probation officers. In late 1994 it became a full-scale initiative, aided by a Federal grant. Now in Boston there are 50 police officers and 50 probation officers riding the streets seven nights a week. Moving into the streets, using gang language and style, the teams have learned that the large majority of gang members are motivated, at some level, to respond to credible authority. More demanding terms of probation -- notably curfews and association rules for offenders, as well as night street presence backed by police -- have changed the impact of the probation department's work. The combination of mentoring and enforcement, along with authentic use of the probation officer's personality, have created the opportunity for violent youth to communicate with the officer and make constructive choices. In the age group targeted by the program, the homicide rate has decreased 76 percent in the last 2 years. Also during this period there have been no juvenile gun-related or knife-related homicides in Boston.