B Factories are particle colliders at which specific subatomic particles - B mesons - are produced abundantly. The purpose is to study the properties of their decays in great detail in order to shed light on a mystery of eminently larger scale: why do we live in a universe composed of anti-matter? This book introduces readers to the physics laws of the CP asymmetry, touching on experimental requirements needed to perform such measurements at the subatomic level, and illustrating the main findings of the contemporary B Factories.