The submitted doctoral thesis is an attempt to describe the nature and of the development of Brentano's theory of judgment. This description is followed by an introduction to the further development of Brentano's theory in the work of Brentano's most distinguished students Kazimierz Twardowski (1866-1938), Alexius Meinong (1853-1920), Anton Marty (1843-1914) and Edmund Husserl (1859-1938). The thesis is divided into five parts: The first part is dedicated to the explanation of Brentano's theory of judgment and starts with an interpretation of Brentano's two early books on Aristotle - On the several senses of Being in Aristotle (1862) and The Psychology of Aristotle (1867). The thesis presents Brentano's understanding of "being" in the sense of truth, his interpretation of the Aristotelian categories, his theory of parts and wholes, and his theory of intentionality and self-consciousness. Our interpretation then proceeds to Brentano's most known work, i.e. to Psychology from an Empirical Standpoint (1874), and presents the basic concept of this book, the concept of psychical phenomena. The resulting classification of psychical phenomena into three kinds introduces judgments as a kind of psychical phenomenon whose main feature consists in existential affirmation or rejection of an intentional object....