Everybody knows about the NYPD’s breathtaking crime-fighting successes over the last decade. Less well known is that NYPD-trained police chiefs are taking over police departments across the country, bringing with them the methods that worked so well in Gotham – above all, data-driven policing – and getting similar results.

This NYPD diaspora has reached at least a dozen American cities. They range in size from giant Los Angeles, where former NYPD commissioner William Bratton has cut violent crime by 18% since becoming police chief two years ago (despite staffing levels proportionately far below those of other big-city forces) to smaller Sarasota, Fla., where former Queens precinct commander Peter Abbott has slashed crime by double digits over the same period. But hands-on, New York-bred police leadership has made the biggest difference to date in Miami and Providence.

Miami Police Chief John Timoney started his career in the rough-and-tumble South Bronx during the early ’70s. Later, as chief of departments and first deputy commissioner under Bratton, Mr. Timoney played a key role in the force’s transformation. He went on to become Philadelphia’s top cop from 1998 to 2002, when the city’s homicide rate fell by one-third.

In January 2003, Mayor Manny Diaz named Mr. Timoney chief of the Miami police, a force with a reputation as a haven for trigger-happy cops. On the day of Mr. Timoney’s swearing-in, a federal criminal trial began against 13 Miami cops on charges resulting from questionable shootings. Mr. Timoney swiftly revamped firearms training, tightened use-of-force rules, and equipped many officers with nonlethal weapons such as stun guns.

Result: the department recently went 20 months without any officer shooting a single bullet, a statistic no other major urban police force can match. (The streak ended in September during an armed robbery, but a new one has been building since.) What made the record truly impressive, though, was that a 30% increase in arrests and an 8% drop in crime accompanied it. The Miami Herald, once one of the Miami police’s sharpest critics, has glowingly praised the department’s turnaround, emphasizing its positive effects on police-community relations.

In January 2003, another NYPD-associated crime fighter, Dean Esserman, took the helm of another troubled force, this one in Providence, R.I. A former Brooklyn assistant district attorney, Mr. Esserman served as general counsel to the New York Transit Police and later advised then-NYPD boss Bratton on corruption, before becoming chief of police in Stamford, Conn. None of these jobs, though, posed problems comparable with those he would face in Providence.

For years, notoriously corrupt Mayor “Buddy” Cianci ran the city. The police even went by the nickname “Buddy’s Boys.” The Feds’ Operation Plunder Dome sent Cianci up the river. During the trial, his former police chief, Urbano Prignano, testified in court to widespread official misconduct, some involving Buddy’s Boys. Racial tensions also simmered in the city, coming to the boil in January 2000 after two white officers shot and killed a black off-duty cop. Crime climbed between the late 1990s and 2002.

Mr. Esserman quickly introduced New York style police tactics, including an aggressive task force (working with federal prosecutors) that removed weapons from the streets in record numbers and, even more important, a Compstat (computerized statistics) management-accountability system that has focused the whole department’s attention on crime reduction and held commanders responsible for achieving it. Serious crime has fallen dramatically – 13% in 2003 and 12% in 2004 – and police morale has soared. Mr. Esserman has replaced most of the Cianci-era commanders with his own trusted people. And he’s improved relations with minorities, in part by opening new police substations in minority neighborhoods.

Before the 1990s, the belief held in both policing and political circles was that crime resulted from factors beyond anyone’s control, and that police could do little to influence crime rates. Gotham’s crime turnaround – which continues under the current commissioner, Ray Kelly – shattered that myth. The New York-bred police chiefs at work in other American cities continue to prove that, properly led, cops can cut crime.

Mr. Upton Sahm works for the Manhattan Institute.Adapted from the new issue of City Journal.