The history of the Queen's Gambit is connected with the very beginnings of modern chess.  The opening being cited in the earliest published books on the science game, such as the Göttingen manuscript (1490) and the books of Ruy Lopez (1561) and Salvio (1604). The so-called Queen's Gambit Declined - or refused - is, together with the Slav, the main defense in the universe of Queenside openings, and shares with the aforementioned defense a well earned reputation for being a reliable and very solid scheme. To make a book considering each and every possibility arising from the opening position of the Queen's Gambit Declined is a cyclopean task that would demand many volumes like the present one.  Instead, the author's aim was to present a simpler repertoire, with no more than one or two variation options for each important position (in the latter case we presented a more positional and a more aggressive line, although in many cases these boundaries are blurred).  The last section of the book  is devoted to the other possible schemes starting from different white moves on their third or fourth move. Here the chapters on the Catalan order 3.g3, which is among the fashionable lines at the master level, and the move 4.e3 (preceded by a knight move to the third rank) are highlighted. Each section presented here is composed of several chapters in which theory is developed with an emphasis on the most modern choices in practice. At the end of each chapter the author presented analyzed games that expose the most common ideas in middlegames.  We hope that by the end of reading this material the reader will not only have incorporated some new ideas into his repertoire - and perhaps changed the idea that the Queen's Gambit Declined is a passive defense - but also have contributed to his general knowledge of chess.