Of the 102 cases, 19 undercover cases were studied intensively. Judicial records of these 19 cases were examined and police officials, prosecutors, and judges were interviewed. In 7 of the 19 cases, undercover action did not start at all for varied reasons. Only the remaining 12 cases could be used to reach conclusions about the effectiveness of undercover policing. The research showed most undercover cases involved drug production, dealing, or smuggling. In many cases, organized crime was involved. Undercover action yielded no relevant information in seven cases but provided relevant information in the remaining five cases. In four of the five cases, the information was used in criminal investigation and prosecution. In three of the five cases, undercover-based information was used in court. Goals of undercover policing were reached in only one case, whereas goals were partially achieved in the remaining four cases. The authors conclude that undercover policing is a very complex process that can be effective where traditional investigative methods have failed. They note, however, that success in undercover policing is not guaranteed. Additional information on the research is appended. References, tables, and figures