‘Understanding the crime drop’ explains that the downward trend has not been confined to particular countries. Nor is it a short-term blip, but has been sustained over a significant period of time, even during periods of great economic turbulence. There is no simple explanation for the rise or fall of crime. It is a combination of factors, including matters of political economy, social inequality, changes in our routine activities, and, more recently, greater attention given to security and crime prevention, which most likely explains the observed trends. However, the role of the Internet is also explored. Do our main measures of crime underestimate just how much crime is taking place?