If you want to play like the best players in the world then playing the Queen’s Gambit Declined is the right choice. Learning it, though, is a difficult process, as it involves a certain amount of knowledge that you won’t find easy. It is not regarded as a particularly sharp opening, but missing one small detail can easily land you in a passive position. Although books on the subject are rare, when we look at all the matches for the World Championship we see that the Queen’s Gambit Declined has always been one of the most popular openings, thus knowledge of the positions arising is the knowledge of the best players. A combination of the Queen’s Gambit Declined and Nimzo-Indian is considered one of best ways to play against 1.d4, 1.c4 or 1.Nf3.