Errors of justice are a serious problem, and the police contribute substantially to them. Much can be done to reduce these errors, involving overreaction, underreaction, and misreaction that imposes either due process errors on the arrested or errors of impunity on the community, or both. The sources, severity, and frequency of these errors vary considerably, and they vary by circumstance and the characteristics of the victim, suspect, and community. Dealing with them effectively begins with understanding these variants and the costs, both social and fiscal, of each type of error on the community. Police legitimacy is likely to be enhanced in the process.