This work analyzes the transcendental relevance of intersubjectivity, arguing that an intersubjective transformation of transcendental philosophy can already be found in phenomenology, and especially in Husserl. Husserl eventually came to believe that an analysis of transcendental subjectivity was a "conditio sine qua non" for a phenomenological philosophy. Drawing on both published and unpublished manuscripts, the book examines his reasons for this conviction and delivers a detailed analysis of his radical and complex concept of intersubjectivity, showing that precisely his reflections on transcendental intersubjectivity are capable of clarifying his phenomenological core-concepts, thus making possible a new understanding of his philosophy. Against this background, the book then attempts to establish the extent to which the phenomenological approach to intersubjectivity can contribute to the current discussions of intersubjectivity. This is achieved through a systematic confrontation with the language-pragmatical positions of Apel and Habermas.