https://www.amazon.com/Queens-Gambit-Declined-Matthew-Sadler/dp/1857442563
Published almost 17 years ago. Still the best learning tool for the Queen's gambit declined by a long shot, as well as one of the 3-4 best openings' books ever written.
The author is honest enough to credit the late Mark Dvoretsky with the minority attack part of the book (which is absolutely top notch).
Wasn't that written about a quarter of a century ago?>>>
Yes but the basic principles remain the same and any improvements and new lines since that time don't affect things for a beginner. I found Marovic's book to be one of the best three or four openings books I've ever read and still occasionally refer to it. There are one or two very slight problems with the indexing, making it difficult sometimes to find one or two obscure sub-variations, but that's about the extent of my objections. In principle it discusses strategy resulting from basic variations white can play, by reference to annotated master games. It's written mainly from white's p.o.v. but it still provides enough info for players of the black side to decide which QGD variation they're going to use. It does rather skip over variations that were out of fashion in the 1990s though, like for instance, some variations of Lasker's Defence or the Old Tartakower, where back plays Nbd7 before b6, which seem to be slightly more played now. And it's a bit hazy regarding the more modern lines of the Tartakower where white delays cd by making waiting moves, but there are still master games to refer to. It covers Capablanca's or the Orthodox Defence reasonably well, the Cambridge Springs very well and also that variation with an early Bb4, which is very sharp, and so on. Occasionally I find that a hybrid crops up that I can't directly refer to in that book but not often and usually as a result of creative play by an opponent. Mainly as a result of that book I've become reasonably strong against the Slav and look forward to playing against it.