This book emerged from the research project Dealing Reasonably with Blurred Boundaries: Vagueness and Indeterminacy as a Challenge for Philosophy and Law. The project spanned four years and was supported by a research grant from the Volkswagen Foundation within the funding initiative ‘Key Issues in the Humanities’. The main aims of the project were to identify and systematize phenomena of vagueness and indeterminacy in different fields of application, to examine their semantics, ontology, and epistemology, and to develop procedures of dealing reasonably with blurred boundaries. Another output of this project is the volume Vagueness in Psychiatry, published in parallel with the present book by Oxford University Press (Keil et al. 2016). We are indebted to Marc Andree Weber, who commented on all chapters and assisted us with the final editing and preparation of the manuscript. Eric J. Engstrom meticulously copy- edited the introduction and two chapters (8 and 9). David Lanius read a draft of the introduction and made a number of helpful suggestions. Throughout the editing and publication period, it was an immense pleasure to work with Nicole Leyland, Natasha Flemming, and Elinor Shields at Oxford University Press.