In the course of these efforts, social scientists have developed standards for assessing claims that some characteristic or condition causes crime and juvenile delinquency. Such standards require that causal claims be backed up with evidence to show an association, to eliminate the possibility of spuriousness, and to establish a causal order. Causal claims must also be preceded by a concerted effort to acquire data representative of the populations under study and to create reliable measures of variables. Even when standards have been taken into account, there may be divergent views about mechanisms or processes through which the causal relationship is established and different theorists may identify different intervening variables. It is also important to specify circumstances of sample, setting, and time that may affect the causal relationship and to have a rudimentary understanding of these circumstances, as most criticisms of research focus on the failure to take one or more of them into account. Biological research on causes of crime and delinquency is reviewed, and the development of psychoanalytic and psychological schools of thought on juvenile delinquency is discussed. The authors note that the concept of the psychopath and attempts to measure dimensions of the psychopathic personality have not advanced the understanding of crime and juvenile delinquency and that delinquent behavior is primarily learned behavior. 58 references and 2 figures