General Introduction.- Elements of Environmental Decoherence.- The Meaning of Decoherence*.- Theoretical Aspects.- Continuous Fuzzy Measurement of Energy: Realization and Application.- Slow Decoherence of Superpositions of Macroscopically Distinct States.- Grey Solitons in Bose-Einstein Condensates as Mesoscopic Particles.- Decoherence Through Coupling to the Radiation Field.- States, Symmetries and Superselection.- Decoherence in Situations Involving the Gravitational Field.- Moving Quantum Agents in a Finite Environment.- Mathematical Aspects of Decoherence.- Decoherence and Continuous Measurements: Phenomenology and Models.- The Problem of Decoherence and the EPR-Paradox.- Asymptotically Disjoint Quantum States.- Experiments.- Dynamical Localization and Decoherence.- Quantum Cryptography and Long Distance Bell Experiments: How to Control Decoherence.- Exploration of the Fundamentals of Quantum Mechanics by Charged Particle Interferometry.- Alternative Approaches.- Single Ions in Paul Traps.- Time-Convolutionless Stochastic Unraveling of Non-Markovian Quantum Master Equations.- Emergence of Classicality: From Collapse Phenomenologies to Hybrid Dynamics.- EEQT - Formalism and Applications.- An Application of EEQT: Tunneling Times.- Conceptual and Epistemoligical Issues.- Non-Markovian Quantum State Diffusion and Open System Dynamics.- Quantum Theory Without Waves: A Way of Eliminating Quantum Mechanical Paradoxes?.- Decoherence as an Irreversible Process.- Many Minds and Single Mind Interpretations of Quantum Theory.- Decoherence and Einselection.