Perpetrators of criminal acts are influenced by a combination of biological, psychological, social, and situational factors. Social and situational factors act more strongly upon marginal personalities characterized by self-centeredness, aggression, and weakness or absence of natural affections. Some physical and psychological traits appear to be part of the criminal personality (e.g., mesomorphism, athletic body build, impulsive and aggressive temperament, mistrust of others, adventurism, status-seeking, and a childhood spent in a home without affection with parents without moral principles). A typology of criminals can be also etiological, and a phenomenological-psychological approach offers some insights into the psychodynamics of the deviant personality. Some scientists explore criminal motivation through use of psychoanalysis and behavioral psychology with its diagnostic tools consisting of psychological tests, psychometric techiques, and personality evaluation. Biological aspects that have been examined as factors of the criminal personality include sex (the numbers of male offenders has always exceeded by far that of female offenders at all times and places);age (criminality decreases with age); brain damage and mental illness (e.g., epilepsy); electroencephalographic anomalies; and endocrine dysfunctions. Genetic abnormalities (e.g., the XYY and XXY, or Kleinefelder, karyotypes) have been shown as possible correlates to criminal behavior. Psychosociological theories consider several variables significant to criminality: ecology, or environmental design, economic conditions, deviant subcultures, cultural influences and migration and acculturation. The victim-offender relationship and victim crime precipitation are further areas being studied for insight into offender behavior. The broad range of factors showing some correlation with crime suggests a need for multidisciplinary research into the complex phenomenon. A total of 52 references are appended. -in Spanish.