Competency to consent to treatment is an especially critical determination to make in the field of psychiatry. Psychiatric patients are often capable, despite their illness, of self-advocacy. Careful assessments are required to differentiate competent patients from incompetent patients. Moreover, the character of their illness, from psychosis to organic brain disease, has been found to correlate with a lack of competency. The presence of auditory hallucinations or delusions, however, are not pathognomonic of incompetency. Currently, there exists no standardized method to establish competency, either in psychiatric or in medical patients. This is a review of the several instruments developed by various researchers attempting to create one. It finds promise in several questionnaires that have good inter-rater reliability and validity.