In recent years what has come to be called the 'New Mechanism' has emerged as a framework for thinking about the philosophical assumptions underlying many areas of science， especially in sciences such as biology， neuroscience， and psychology。 This book offers a fresh look at the role of mechanisms， by situating novel analyses of central philosophical issues related to mechanisms within a rich historical perspective of the concept of mechanism as well as detailed case studies of biological mechanisms （such as apoptosis）。 It develops a new position， Methodological Mechanism， according to which mechanisms are to be viewed as causal pathways that are theoretically described and are underpinned by networks of difference-making relations。 In contrast to metaphysically inflated accounts， this study characterises mechanism as a concept-in-use in science that is deflationary and metaphysically neutral， but still methodologically useful and central to scientific practice。