This paper begins with a recapitulation of the historical development of analytic theories regarding the nature of anxiety. It stresses the importance of Freud's distinction between primary and secondary anxiety. Primary anxiety is understood as a direct result of such helplessness in a situation of overwhelming excitation as to constitute a traumatic event. Secondary anxiety is defined as a defensive reaction brought about by fear in the face of an internal danger situation. Therefore, the capacity to bear anxiety must be considered in the light of this double orientation. There follows a brief discourse on the origin of instinctual frustration and a consideration of the various theories of aggression. This leads to a discussion of clinical meterial related to the two types of anxiety, illustrating clearly the value of theory to practice. The paper ends with the thesis that experience with anxiety and a mastery of it are necessary for emotional development. Some types of psychic and prepsychotic characters are unable to tolerate anxiety.