The necessity for intensive and productive research in the fields of criminal behavior, juvenile delinquency and correctional administration is self evident. Progress in any field, whether physical or social, ceases when research is meagre or when it is conducted in a superficial manner. Who could imagine the present status of medical science without the intensive physiological and biochemical research on which this profession rests? For a number of reasons, some custodial, others bureaucratic, criminological research involving in-prison populations is neither as frequent nor as intense as is desirable to provide needed data on the complex problem of criminal behavior. Criminological research involves many approaches and many techniques; a good deal of data can be gathered in the community and from the courts. Records, police as well as correctional and psychological tests, can be examined and analyzed. Nevertheless, a necessary adjunct to other research approaches involves interviews with known criminals held in custody in our prisons. Many factors of sociological significance, such as self conception, levels of aspiration, attitudes and motives of offenders, can be measured only by carefully structured in-prison interviewing. While it is true that prison populations are not representative samples of the universe of crime, research among inmates is, at the very least, one primary source of basic criminological data.