Mental health professionals must abide by the legal definitions that apply, use the technical and empirical standards of their professions, and use care regarding the ethical obligations of their professions. These three standards sometimes conflict with one another. The legal procedure for determining competency has five stages: 1) requesting a competency determination, 2) the court-ordered competency evaluation, 3) the judicial determination and disposition, 4) treatment for mental incompetency, and 5) rehearings on competency. Issues arising during this processing include the variations in judicial interpretations of evidence, variations in evaluation methods, the tactical misuse of competency procedures, the inappropriate use of evaluations and incompetency commitments to provide psychiatric treatment, and confusion regarding the legal standard. Among unresolved issues are the use of court orders for evaluations of both competency and insanity, confusion regarding competency to negotiate and to plead, the scope of competency assessments, and the use of mental health professionals to testify about legal competency. Mental health professionals can help improve the use of competency assessments by being familiar with the relevant law and practice, by approaching each assessment as though it is the most important, and by communicating concerns to researchers, legislators, and judges. 60 references.