While illusion plays an important role in life, its significance has been under-emphasized by psychoanalyst who do not regard it as a defense mechanism per say and have tended, with the exception of Winnicott, to leave the concept largely unmentioned. The author speculates about why this might be, defines the term “illusion” in order to discuss the term in the broadest sense, then focuses in on a subset of illusions-those contributing to an individual's sense of safety, power and control-which provide positive benefits-serving protective and adaptive functions-that come at a cost (limiting one's capacity to empathize with others, refusal to take responsibility for one's own actions, etc). The author identifies three particular types of illusions-heroic, magical and illusions of control-the latter of which is investigated in great detail relative to the way in which interpersonal relations are much effected by the illusion that one party can seize control of another's actions (“make them do as one pleases”). Clinical examples are provided that illustrate instances when patients have attempted to exert unreasonable amount of control over the analyst.