The essays in this volume discuss the unity and multiplicity of the logos in the cosmos, a question central to mediaeval cosmological and metaphysical speculation. Beyond the usual juxtaposition of henology and ontology, which still dominates in the study of mediaeval conceptions of natura, an attempt is made here to trace some of the lines of argument that formed the basis for a justification of the view that nature as a whole is to be understood as the unfolding and manifestation (explicatio) of an artificial-creative causal principle. A central role is played here by the polemics around the so-called Liber de causis from historical and systematic perspectives. Finally in connection with the discussion of classical mediaeval positions, the possibilty of a productive dialogue with contemporary conceptions is discussed, with the aim of rehabilitating the classical conception of the logos, for example in the works of authors such as H.-G. Gadamer andf J.-L. Nancy.