Just as the hardware of a large computer system requires a large program, often called software or an operating system (OS), to supervise and control its performance, so too do human beings require a mind to control the brain. Our OS, however, is hardwired in neuronal circuitry and also involves the endocrine system. Much evidence attests to the built-in nature and existence of our OS. Examples are our abilities (1) to conceive ideas, (2) to process them internally and symbolically, (3) to express them in any of several modes (e.g., as verbal strings, as visual images, in sign language, in body language), (4) to dream. Some of the probable anatomical components of the human OS are identified and some indications of its systematic effects on consciousness are discussed. Some research relating psychopathology to the OS is cited.