There are few more unsettling philosophical questions than this: What happens in attempts to reduce some properties to some other more fundamental properties? Reflection on this question inevitably touches on very deep issues about ourselves, our own interactions with the world and each other, and our very understanding of what there is and what goes on around us. If we cannot command a clear view of these deep issues, then very many other debates in contemporary philosophy seem to lose traction - think of causation, laws of nature, explanation, consciousness, personal identity, intentionality, normativity, freedom, responsibility, justice, and so on. Reduction can easily seem to unravel our world. Here, an eminent group of philosophers helps us answer this question. Their novel contributions comfortably span a number of current debates in philosophy and cognitive science: what is the nature of reduction, of reductive explanation, of mental causation? The contributions range from approaches in theoretical metaphysics, over philosophy of the special sciences and physics, to interdisciplinary studies in psychiatry and neurobiology. The authors connect strands in contemporary philosophy that are often treated separately and in combination the chapters allow the reader to see how issues of reduction, explanation and causation mutually constrain each other. The anthology therefore moves the debate further both at the level of contributions to specific debates and at the level of integrating insights from a number of debates.