The basic science of diagnosis and treatment of mental illness is described from the point of view of the practitioner. My experience may be different from psychiatrists in public health, research, and academic settings. I have been at the point of service since 1970 as a medical student, since 1972 as an intern and since 1973 as a licensed medical doctor and since 1977 as a board-certified psychiatrist. The practice of psychiatry changes from place to place and from time to time. Psychiatry is complex and never simple. The complexity is difficult to display fully in only 66 pages. But it is a good starting point for the student, the patient, the family and other "stakeholders," in the process of treating mental illness at the point of service. Administrators and chain of command are at arm's length, or more than arm's length with a different point of view. Pharmaceutical Companies conduct themselves on a different platform with different rules of engagement. Thank you for your time and attention. I am here to do no harm, and to help if I can. William Ronald Yee M.D., J.D.