The responsibilities of psychologists and psychiatrists often overlap; both psychologists and psychiatrists can diagnose and evaluate mental illness, provide psychotherapy, and conduct research. Nonetheless, their background and training differ considerably. In general, psychologists are students of the mind and behavior while psychiatrists are experts in mental illness. Psychologists are trained in academia and their highest degree is the doctorate (Ph.D. or Psy.D.) in psychology. They do not prescribe medicine, unless they are certified by the few states that have prescription privileges for psychologists. Moreover, not all psychologists are involved with clinical work. In contrast, psychiatrists are trained in the medical field. They are all physicians, having completed medical school and having obtained an M.D. (or D.O.). Their training is almost entirely clinical and focuses on the evaluation and pharmacological treatment (i.e., medication) of severe mental illness.