An in-depth philosophical reflection on Ornament is substantially unpublished. From this point of view, the endless, multiform continent of decoration turns out to be a probe that calls into question some of our beliefs about the forms of art and the thought that presides over them. In this book, the author follows a double interpretative path: the theoretical-philosophical level, in fact, intersects and dialogues with the historical-critical context. The perspective that leads from Kant to Husserl and then to the debate on the concept of Kunstwollen ('artistic will') that sees Riegl, Panofsky and Sedlmayr as protagonists, meets on its path the perspective that elects among its exemplifying moments: Islamic art, Matisse, the Vienna of Klimt and Loos. During this journey, other great authors of twentieth-century European culture meet, from Simmel to Valéry, from Bloch to Lévi-Strauss, from Hartmann to Focillon, just to name a few. We will discover that the stubborn belief that the Ornament, believed something additional or optional, will conceal the opposite assumption and its alleged marginality will reveal a paradoxical centrality.