This document provides an introduction to psychiatry, beginning with definitions of health, mental health, and mental illness. It then outlines the history of psychiatry from ancient times through the 20th century, including developments during the times of Hippocrates, Rome, the Middle Ages, Renaissance, Enlightenment, and modern psychiatry in the 19th century. The document also briefly discusses the impacts of World War II, fascism, and "Action T4" led by Dr. Karl Brandt, as well as progress made in the field during the late 20th century through the 21st century.