The thought of Alexius Meinong (1853–1920) has a distinguished position within the conceptual space of ontology. He was the first philosopher who tried systematically to develop a quasi-ontological discipline which was intended to be much more general than the metaphysics in the traditional sense. Metaphysics investigates being qua being; and this constitutes only a small part of the domain of the theory of objects (Gegenstandstheorie) as Meinong conceived of it. For – so reads one of Meinong’s most frequently cited theses – the objects considered purely qua objects are neutral concerning their being or non-being. In this book Meinong’s theory of objects is presented in its historical development and investigated within the context of his theory of intentionality. This connection is justified because the real motivation behind Meinong’s introduction of entities "beyond being and non being" lies in the philosophical puzzles of the theory of intentionality.