Why didn't the matter in our Universe annihilate with antimatter immediately after its creation? This book presents theoretical tools necessary to understand this phenomenon. Reflecting the recent explosion of new results, this second edition has been substantially expanded. It introduces charge conjugation, parity and time reversal, before describing the Kobayashi-Maskawa (KM) theory for CP violation and our understanding of CP violation in kaon decays. It reveals how the discovery of B mesons has provided a new laboratory to study CP violation with KM theory predicting large asymmetries, and discusses how these predictions have been confirmed since the first edition of this book. This lead to M. Kobayashi and T. Maskawa receiving the 2008 Nobel Prize for Physics. Later chapters describe the search for a new theory of nature's fundamental dynamics. This book is suitable for researchers in high energy, atomic and nuclear physics and the history and philosophy of science.