Husserl's definition of consciousness in terms of intentionality marks a revolutionary innovation in the history of modern philosophy. It solves a problem which, on the grounds of the traditional modern conception of consciousness, proved hopelessly enigmatic; to say the least, the problem in question is opened to promising theoretical treatment. Hence, it appears opportune to consider Husserl's theory of intentionality historically, though, to be sure, the theory of intentionality must ultimately be judged on its own merits. Its validity can only depend upon its satisfactorily accounting for the fundamental structure of consciousness. Still, to present it historically brings forth its full significance in the most striking fashion.