The concepts of repression, defense, and anxiety have become the core of modern analytic and psychiatric theory. The development of some ideas has been so complex, contradictory, and uneven as to make it most difficult to gain clear understanding. This is especially true of the 'repression-defense theory'. 'Defense' refers to all forms of ego protection against inner impulses perceived as dangerous. The term 'repression' is sometimes used with that same meaning. It is also used to mean the keeping of ideas from consciousness, through isolation, undoing, and reaction-formation, and in other ways. 'Repression' can also mean ego protection through emotional inhibition. Finally, it is sometimes applied to hysterical amnesia, forgetting. Sharper definition and usage of the word will contribute to clearer thinking and improved technique.