The agelong battle between sociologists and psychologists for dominance in criminology is viewed as meaningless, because psychology was always part of criminology. Social conditions alone cannot explain criminal behavior (e.g., deprivation does not cause all poor people to commit crimes, but only a small percentage). The article suggests that institutional arrangements are mediated through individual human action. Further psychological findings form a solid base upon which new principles of social structure and structural change are built. It further suggests that existing theories of crime explain data with the principles that motivate an individual to violate the law (e.g., deprivation, lack of opportunity, marginality, participation in a subculture). The context is social, but the subject under scrutiny is individual (or psychological). Criminological theories by sociologists but with psychological components include social disorganization; opportunity or strain; and differential association. Even the labeling theory, seemingly concerned with society's stigmatization of the socalled criminal, is based on the labelled individual's reactions and responses to the label assigned to him. The article lists other criminological theories based on psychological research including social learning theory (in which crime is viewed as a subset of a larger psychological construct, that of aggression). Concentrating on etiology (how criminals came to crime) and description (how they currently function as criminals), the study examines the relationship between psychological disorder and criminal behavior, noting that the evidence, based on surveys of prison populations and former mental patients, is still inconclusive. The characteristics of criminal offenders are also analyzed, based chiefly on the Minnesota Multiphasic Personality Inventory. Two main types (overcontrolled and undercontrolled aggressive) share such characteristics as impulsivity, lower-than-average IQ, need for immediate gratification, as well as a non-MMPI characteristic, that of temporal orientation. A list of 125 references is appended.