This book offers the unique possibility of tackling the problem of hadronic deconfinement from different perspectives. After general introductions to the physical issues, from both the theoretical and the experimental point of view, the book presents the most recent expertise on field theory approaches to the QCD phase diagram, many-body techniques and applications, the dynamics of phase transitions, and phenomenological analysis of relativistic heavy ion collisions.One of the major goals of this book is to promote interchange among those fields of research, which have traditionally been cultivated by different communities of physicists. The contributions in the book help in obtaining deep comprehension of this new state of matter, a system of deconfined quarks and gluons. At the same time the book offers a few examples of how the seeds of the deconfined state are looked for in the phenomenological analysis of the observables measured in relativistic heavy ion collisions. The main topics are dealt with in a pedagogical style, suitable for beginners as well as experienced researchers.