Written for graduate students, lecturers and readers with research interests, this book provides a comprehensive and self-contained introduction into the main ideas and concepts of the quantum theory of open system, in addition to developing advanced analytical methods and computer simulation techniques. 'This book covers a large set of topics, normally not covered in standard physics curricula ... I recommend this book to physicists interested in widening their horizons in the directions covered by the book ... I do not know of any other source providing such a systematic and well written introduction into this area of research.'