CRIMINOLOGICAL TWIN INVESTIGATIONS BY JOHANNES LANGE, A.M. LEGRAS, A. J. ROSANOFF AND OTHERS, FRIEDRICH STUMPFL, HEINRICH KRANZ, C. A. BORGSTRAOM, SHUFU YOSHIMASU, PEKKA TIENARI, AND ODD STEFFEN DALGAARD AND EJNAR KRINGLEN ARE CRITICALLY EXAMINED. IT IS CONCLUDED THAT NO STUDY AS OF 1977 HAS PROVIDED CONCLUSIVE EVIDENCE OF THE DOMINANCE OF GENETIC OVER ENVIRONMENTAL FACTORS IN THE GENESIS OF CRIMINALITY. GIVEN THE NATURE OF THE GENETIC AND ENVIRONMENTAL FACTS, IT IS STILL DEEMED AN APPROPRIATE A PRIORI HYPOTHESIS THAT HEREDITY AND ENVIRONMENT ALWAYS INTERACT IN A DYNAMIC FASHION TO BRING ABOUT AND SHAPE CRIMINAL BEHAVIOR, AND THAT BOTH THE MUTUAL INTERACTION AND THE MUTUAL STRENGTH OF THE TWO FACTORS FORM A CONTINUOUS DIMENSION FOR ALL PERSONS AND SITUATIONS. FUTURE RESEARCH WILL HAVE TO ESTABLISH THE DETAILS OF THE CORRELATIONS IN THIS FIELD. IN GENERAL, IT IS CONCLUDED THAT CRIMINALITY, DEFINED AS A SOCIOLEGAL CONCEPT, CAN ONLY BE STUDIED FROM A GENETIC POINT OF VIEW AS LONG AS IT IS CLOSELY ASSOCIATED WITH A WELL-DEFINED SOMATIC OR PSYCHOLOGICAL STATE. (AUTHOR ABSTRACT MODIFIED--RCB)