The author discusses how plainclothes investigations have gone through cycles of popularity and decline. In the last 25 years, research has examined the productivity of detectives, including the goals of investigations, changes police officials have made in investigative operations, and changes in the management of criminal investigation. The author concludes that the reforms have severe limitations; these limitations are summarized with three laws of investigations. The first law of investigations is that reliance on cheaply obtained information results in few solutions, but to obtain many solutions, investigators must obtain expensive information. The second law of investigations is that the direction of all investigations is largely out of the investigators' control; and the more control that is desired, the more expensive the investigation will become. The third law of investigations is that the circumstances that call for specialization also call for decentralization, and the circumstances that require centralization require despecialization. A recurring theme of this paper is that the management of criminal investigations involves conflicting difficulties; addressing one almost ensures that the other will get worse, thus forcing change in another direction. 37 references