Understanding Ideology enables the reader to recognize public expressions of an ideology,thereby avoiding gullibility and the consequences of ignorance. Of Karl Mannheim's classic dual conception of ideology, a Marxist-Freudian orientation is adopted. Supporting this is a critical conception of social alienation with aggressivity, narcissism, and socialization providing the psychological foundation for establishing any ideology. Operative in ideology are the same psychically defensive mechanisms Freud found in wishful dreams, neurotic repression, paranoia and mythology. Various forms of fallacious reasoning and propaganda sustain ideology. Finally dealt with is the possibility of escaping ideology as well as its difference from science.