The present Volume 4 of the Vienna Circle Yearbook is dedicated to Otto Neurath, one of the leading figures of the Vienna Circle and one of last polymaths representative of the vanished culture from which the Circle emerged. Situating Neurath's work between the topoi of Encyclopedism - as a theoretical, scientific tool of the ‘unfinished' project of (post-) enlightenment - and Utopianism - as the resolve to work for the systematic improvement of society and science - this volume presents the most recent research as well as critical and updated surveys and assessments of Neurath's many-faceted and impressive life work. The contributions range from history and philosophy of science, epistemology, sociology and economics to pictorial statistics (ISOTYPE) and museology. Special attention is given to Neurath's methodological holism and epistemological naturalism, as well as to the interrelations of the different disciplines in Neurath's conception of the Unity of Science. Most contributors agree that the historical and systematic reconstruction of Neurath's conception of science leads to issues of crucial relevance to the ongoing task of sharpening the instrument that is science for its responsible application in the natural and social world. The volume also includes Neurath's previously unpublished full manuscript on visual education, a report on archival holdings concerning Neurath's work and a review section focusing on recent publications on Neurath and Logical Empiricism. An overview of the activities of the Institute Vienna Circle 1996/97 concludes the volume. Audience: Philosophers in general, philosophers of science and historians of science, and sociologists. The book will also interest scholars specialized in adult education, museology and economics.