Crackdowns represent one of the most widespread developments in policing during the 1980's. Drunk driving, domestic violence, public drug markets, prostitution, and illegal parking have all been targets of publicly-announced police crackdowns. What crackdowns have in common is a short increase in law enforcement resources applied to previously underenforced laws, with the clear goal of deterring misconduct. By constantly changing crackdown targets, police officers can reduce crime more through the accumulation of residual deterrence at several locations than through initial deterrence at a single location. Police crackdowns have three possible tactical elements: presence, sanctions, and media threats. Presence is simply an increased ratio of police officers per potential offender. Sanctions denote coercive police actions, while media threats are announced intentions to increase the certainty of sanctions. Police crackdowns take two frequently overlapping forms. One is a policy change about how to handle specific offenses, such as arresting wife beaters rather than counseling them. The other is increased police presence in specific geographic areas. Evidence indicates that some crackdowns initially deter or at least displace some kinds of offenses. However, it is hard to sustain many crackdowns over a long period because police eventually start backing off or potential offenders gradually realize the chances of being caught are not as great as they had thought. Crackdown decay, a gradual decline from initial changes, is discussed, and case studies of police crackdowns are noted.