The study reviews and evaluates current scientific evidence about the validity of polygraph testing. It is not possible to establish an overall measure of test validity -- first, due to the complexity of such testing; and, second, due to the wide range of results in researching such testing. The available research evidence does not support polygraph testing for personnel security screening. Polygraph testing is valid only in the area of investigations of specific criminal incidents. Even here, findings about polygraph validity must be qualified. The polygraph test detects deception better than chance, but with significant error rates. Countermeasures may affect validity to suggest false negatives. The accuracy obtained in one situation or study may not generalize to different situations or to different types of persons being tested. Appendixes include the informed consent form used by the Federal Government, the result of the survey of Federal Government polygraph use, the coding form for analysis of studies, and a glossary of key terms. Tables and over 200 references are provided. (Author modified summary)