The mental health professional's role in determining patient competency is an ever-increasing one, and is increasingly being researched and scrutinized. Competence is a legal concept, and the determination of incompetence can only be established through the judicial system. Mental health professionals, nevertheless, remain intimately involved in these decisions since the courts rely heavily on expert witness evidence (Iris, 1988). This review will be illustrative and not complete (see Moye, 1996 or Grisso, 1994 for more thorough reviews), and will present and critique several research studies of competency. Finally, some guidelines will be presented.