I have not written any books on topics that pertain to my more narrowly defined philosophical interests – neither on the theoretical foundations of sociology, nor on the formal-pragmatic conception of language and rationality, nor on discourse ethics or political philosophy, or on the status of post-metaphysical thinking. This peculiar circumstance only becomes apparent to me in retrospect; and I do not know whether I should regard it merely as a deficit. On June 18, 2009, the philosopher and sociologist Jürgen Habermas celebrates his 80th birthday. On this occasion, he has compiled a systematic selection of important texts, some of which are unpublished, that reveal the philosophical core of his extensive work. Jürgen Habermas has written a detailed introduction for each volume, in which he discusses the themes.