Causality - the concept of cause and effect - has long been viewed by philosophers, from Aristotle to Kant, as fundamental to our understanding of the universe. In this book we construct a theory of physics based on causality. We discover that the simplest causal network, based on Reichenbach's principle of common cause, exactly describes the Dirac equation and is consistent with both special relativity and quantum mechanical statistics. Are the "elementary" particles and "fundamental" laws of physics emergent from causality? Many historical philosophers would have perhaps taken this for...