The report's first section summarizes the history and current operations of the Witness Protection Program and reviews prior evaluations, noting that such research is sparse. The paper describes the psychological evaluations and interviews conducted with 41 prisoner-witnesses. This all-male sample ranged in age from 24 to 58, had an average of 10.4 years of education, and was predominantly white and raised in Catholic intact families. Memory and recall did not appear to be a problem for this group when called to testify. A major difficulty, however, was isolation from family and friends, because security considerations made visits difficult to schedule. About 64 percent reported having thought about changing their minds regarding cooperation with the authorities, and for most, this feeling occurred within 1 year of their admission into the program. One reason offered for continued cooperation was the perception that no alternatives were available. Nearly two-thirds said they would not encourage others to take a similar course in breaking from organized crime. Over half said they had not felt endangered since their involvement with the program, although most claimed friends or other witnesses knew where they were. The survey also collected data on past legitimate employment, health, criminal involvement of family members, early criminal behavior, perceptions of organized crime, threats, and psychological attributes. Overall, the interviews revealed that the government bureaucracy was not always sensitive to individual personalities and problems of witnesses. The paper develops four typologies of protected witnesses to guide law enforcement agencies in their decisions on admissions, witness relocation, witness adjustment potential, and the need for specialized treatment. Tables, 12 references, and explanations of the study's methodology are supplied.