This text deals with the theory behind quantum mechanics and also shows how the theory applies to contemporary physics. In addition to incorporating suggested improvements from many users, this edition is thoroughly updated - not only in terms of physics research but also in terms of how quantum mechanics is taught today. The book provides a unified approach to quantum dynamics giving students a broad perspective, and showing the derivations of various pictures and representations of quantum dynamics without losing sight of the overarching common features of the theory. This graduated approach introduces matrix methods and symmetry arguments at an elementary level, before the systematic study of the abstract theory of vector spaces and operators. Theory is emphasized in three stages - explicit elementary examples, essential concepts for the interpretation of experiments in subatomic physics, and general abstract formulation in terms of integral equations and scattering operators