Fritz Redl (1902-1988) originated the life space model of therapeutic intervention with children who display angry and defiant behavior. His methods were honed by decades of direct work with highly aggressive youth. Redl observed that the same surface behavior could spring from very different underlying problems, thus requiring different interventions. In this classic article, Redl identified four distinct problems that could trigger defiant behavior. The four patterns he labeled have been validated by subsequent research: 1) "developmental defiance" is the normal quest for autonomy; 2) "defiance as a wrapping" is aggression secondary to mental disorders such as autism or depression; 3) "reactive defiance" is angry aggression; and 4) "the defiant ego" is instrumental aggression. (Contains 3 notes.)