The Dilute Bose Gas in 3D -- The Dilute Bose Gas in 2D -- Generalized Poincaré Inequalities -- Bose-Einstein Condensation and Superfluidity for Homogeneous Gases -- Gross-Pitaevskii Equation for Trapped Bosons -- Bose-Einstein Condensation and Superfluidity for Dilute Trapped Gases -- One-Dimensional Behavior of Dilute Bose Gases in Traps -- Two-Dimensional Behavior in Disc-Shaped Traps -- The Charged Bose Gas, the One- and Two-Component Cases -- Bose-Einstein Quantum Phase Transition in an Optical Lattice Model.This book contains a unique survey of the mathematically rigorous results about the quantum-mechanical many-body problem that have been obtained by the authors in the past seven years. It addresses a topic that is not only rich mathematically, using a large variety of techniques in mathematical analysis, but is also one with strong ties to current experiments on ultra-cold Bose gases and Bose-Einstein condensation. The book provides a pedagogical entry into an active area of ongoing research for both graduate students and researchers. It is an outgrowth of a course given by the authors for graduate students and post-doctoral researchers at the Oberwolfach Research Institute in 2004. The book also provides a coherent summary of the field and a reference for mathematicians and physicists active in research on quantum mechanics.