Dispositions are everywhere. We say that a wall is hard, that water quenches thirst and is transparent, that dogs can swim and oak trees can let their leaves fall, and that acid has the power to corrode metals. All these statements express attributions of dispositions, be they physical, physiological or psychological, yet there is much philosophical debate about how far, if at all, dispositional predicates can have complete meaning or figure in causal explanations. This collection of essays, by leading international researchers, examine the case for realism with respect to dispositions and causal powers in both metaphysics and science. Among the issues debated in this book is whether dispositions can be analyzed in terms of conditionals, whether all dispositions have a so-called categorical basis and, if they do, what is the relation between the disposition and its basis.