Defeasibility, most generally speaking, means that given some set of conditions A, something else B will hold, unless or until defeating conditions C apply. While the term was introduced into philosophy by legal philosopher H.L.A. Hart in 1949, today, the concept of defeasibility is employed in many different areas of philosophy. This volume for the first time brings together contributions on defeasibility from epistemology (Mikael Janvid, Klemens Kappel, Hannes Ole Matthiessen, Marcus Willaschek, Michael Williams), legal philosophy (Frederick Schauer) and ethics and the philosophy of action (Claudia Blöser, R. Jay Wallace, Michael Quante and Katarzyna Paprzycka). The volume ends with an extensive bibliography (by Michael de Araujo Kurth).