This open-access book addresses the following questions: how does the polarization of a particle, i.e., the angular momentum state in which it is produced, manifest itself in nature? What are the concepts and tools needed to perform rigorous measurements providing complete and unambiguous physical information?Polarization measurements are important because they reflect the nature and coupling properties of a particle and provide unique insights into the underlying fundamental interactions, playing a central role in the study and understanding of the mechanisms of particle production.Besides...