The developments of the concepts of "defense" and "ego" in the last thirty years are surveyed. The question of pathogenicity of defense mechanisms is examined; their organization and role in normal psychic life and in adaptation are noted. The role of the defensive organization and of autonomous ego functions is discussed from the standpoint of technique. In psychoanalytic technique the difference is stressed between fundamental principles, practical rules, and the body of psychoanalytic knowledge. Some clinical vignettes illustrate the author's views.