My basic research has identified the fact that crime is highly concentrated at micro geographic places like street segments. I call this the “law of crime concentration at places” because the concentration is fairly consistent across cities. In larger cities, about 1 percent of streets produce 25 percent of crime, and about 5 percent of streets produce 50 percent of crime. These crime concentrations, or crime hot spots, are relatively stable across time. This basic research has led to a series of field experiments that increase police presence at crime hots spots. These field experiments have provided strong evidence that hot spots policing can reduce crime, without displacing crime to nearby areas. My recent research has focused in particular on the characteristics of these crime hot spots, and how they differ from places with little crime. We have found that hot spots of crime are not just hot spots of crime, but places where many other problems are concentrated. In turn elements of opportunity are an important predictor of why streets are crime hot spots, but so are social factors such as collective efficacy.