Information theory is the quantitative study of signal transmission. Primarily applicable to information technology and communications engineering, in human communication theory, it serves primarily as a metaphor for linear transmission between human senders and receivers. Although information theory has historical significance, contemporary theories of human communication rarely refer to it directly. Originating in physics, engineering, and mathematics, the theory addresses uncertainty in code systems, message redundancy, noise, channel capacity, and feedback. This entry defines basic concepts from the field, applies these to language and human communication, and summarizes insights about information transmission.