The domain of Psychology and Law belongs more to psychology than to law. Typical studies and publications in the field are psychological in nature, as they are applications of psychology within a legal context. Such studies may influence the practice of law and even legislation, but they are based on the research logic and methodology of psychologists. In general, this is the methodology for empirical research into basic psychological faculties such as perception and memory, automatic and controlled behaviour, logical thinking and problem solving, the formation of complex judgements and decision making. Such empirical studies always involve human subjects and are therefore limited by ethical constraints. Although such constraints by themselves do not seriously hamper the research process, they often constitute a problem when we try to apply the results in a context in which deceit, fraud, theft, robbery, drug trafficking, sexual abuse, rape, torture, and murder are the common themes. For ethical reasons, that context cannot be replicated in the psychological laboratory. It is difficult to create a research design in which human subjects are made to witness or to become victims of a serious crime in an ethically acceptable way. For this reason, the link between psychological research and its application in legal practice is never simple and straightforward.

The parties involved in civil or criminal cases know only too well that their cases are primarily decided on their legal merits. Psychological insights may play a role, but only if there is legal precedent, and in so far as they have clearly demonstrable relevance for the cases at hand. This may explain why the field of psychology and law has developed mainly in the context of actual legal trials; it is based on psychological questions raised in court, the expert testimony presented, and the acceptance or rejection of such testimony by judges and juries. It is virtually impossible for researchers in this field to make significant progress without experience as expert witnesses in actual trials.

One might expect that the progress in the field of psychology and law is achieved by collecting in-depth descriptions of applications in actual trials. But this is not so. Often the scientific literature does not refer to any case in particular; at best it refers only obliquely to cases that the reader is supposed to recognise.