The book focuses on Robert Alexy's theory of constitutional rights. Alexy systematically presented the theory in his seminal book "Theorie der Grundrechte" (1985; Engl. translation "Theory of Constitutional Rights, 2002) and continued to develop it in numerous subsequent articles. Arguably still the most influential theory of constitutional rights, it has found widespread academic support, as well as recognition in several constitutional jurisdictions. On the other hand, it has also been the object of considerable criticism. The aim of this book is to outline the central aspects of Alexy's theory as he sees them, and to further develop the principles of constitutional, fundamental, and human rights by applying a constructive criticism of his theory.