Chess Explained books are not theoretical works in the traditional sense, but more a series of lessons from a chess expert with extensive over-the-board experience with an opening. You will gain an understanding of the opening and the middlegames to which it leads, enabling you to find the right moves and plans in your own games. It is as if you were sitting at the board with a chess coach answering your questions about the plans for both sides, the ideas behind particular moves, and what specific knowledge you need to have.
The Queen's Gambit Declined is one of the most important and popular of chess openings. While an immensely solid and classical choice for Black, it has remained highly topical for more than a century. Both sides have ways to create imbalance and test their opponent's skills and knowledge in a full-blooded struggle. Most of the World Champions have taken both sides of the QGD, with Spassky and Karpov especially notable defenders of Black's cause. In addition to the traditional main lines with Bg5, White has at his disposal the Exchange Variation, and the Bf4 system, both of which can be handled in highly aggressive style if he wishes. Rizzitano covers all these lines and a plethora of other important lines, focusing on the fundamental ideas on which they are based.