Since the mid-1980s, Federal-local collaboration has become a standard feature of law enforcement in most larger U.S. cities. This study examined how collaboration has evolved during two decades of joint crime-fighting against drugs, illegal weapons, and gangs. The study also examined particular collaborations in three cities: San Diego, Detroit, and Memphis. Most of those involved agree that collaboration is a success. Many high-level, large-scale drug and gang investigations were made possible only through Federal collaboration with local prosecutors and police. Collaboration offers many advantages for local police and prosecutors, as well as Federal authorities. These include improved law enforcement coordination, intelligence sharing, and problem solving. Although some believe that the Federal role in local law enforcement has become too great, over the past decade that role has increasingly been defined through consensus-based coordination with local authorities. Collaboration is likely to expand in the future. Most task forces and other collaborations are quite popular with Federal and local law enforcement representatives and prosecutors and enjoy high-level community support.