The volume brings together for the first time original essays by leading philosophers working on powers in relation to metaphysics, philosophy of natural and social science, philosophy of mind and action, epistemology, ethics and social and political philosophy. In each area, the concern is to show how a commitment to real causal powers affects discussion at the level in question. In metaphysics, for example, realism about powers is now recognized as providing an alternative to orthodox accounts of causation, modality, properties and laws. Dispositional realist philosophers of science, meanwhile, argue that a powers ontology allows for a proper account of the nature of scientific explanation. In the philosophy of mind there is the suggestion that agency is best understood in terms of the distinctive powers of human beings.