This paper presents a theory of humor, that certain psychological state which tends to produce laughter. The theory states that humor is fully characterized by three conditions, each of which, separately, is necessary for humor to occur, and all of which, jointly, are sufficient for humor to occur. The conditions of this theory describe a subjective state of apparent emotional absurdity, where the perceived situation is seen as normal, and where, simultaneously, some affective commitment of the perceiver to the way something in the situation ought to be is violated. This theory is explained in detail and its logical properties and empirical consequences are explored. Recognized properties of humor are explained (incongruity, surprise, aggression, emotional transformation, apparent comprehension difficulty, etc.). A wide variety of biological, social/communicational, and other classes of humor-related phenomena are characterized and explained in terms of the theory