The analyst's mistakes are an inevitable aspect of his conduct of psychoanalysis. They result from the inherent uncertainties and ambiguities of the analytic process itself, and from the continuing effect upon analytic technique of the analyst's unresolved conflicts, as manifested in countertransference attitudes and enactments. Variables of clinical experience, skill, and the vicissitudes of the analyst's life also contribute to the susceptibility to error. When the analyst's mistakes result from his active engagement in the psychoanalytic process, they yield important clues for understanding clinical material as well as present potential obstacles to analytic progress.