2. Basic Concepts in the Slav Defence
3. Main- and Sublines of the Slav Defence
4. Slav Defence - Polugaevsky-Torre
5. Tips and Guidelines for Building a Repertoire in the Slav Defence
6. Conclusion – a Summary of Basic Strategies
The basic point of the move 2...c6 is to solidly defend d5, while keeping the diagonal of the light-squared bishop open. There’s also another no less important idea connected to it: starting active counterplay on the queenside with ...dxc4 followed by ...b5. The character of the game can become ultra-sharp (e.g. the Botvinnik Variation) or quiet and positional (e.g. the 3.Nf3 Nf6 4.e3 line). This makes the Slav attractive to players of various levels and playing styles. Both sides can select systems in accordance to their skill and liking.
According to Lev Polugaevsky (see the sample game for more information on this great player), Polish, Russian, Czech, and Yugoslav players made the most significant contributions to the development of 2..c6 – hence the naming Slav Defence. The Slav received several hard tests in World Championship matches. It was particularly favored by Euwe, Botvinnik and Smyslov. From the champions of the new millennium, Anand and Kramnik stand out as exceptional experts.
In the Slav defence Black defends the center and keeps the diagonal of the c8-bishop open (as opposed to the Queen's Gambit Declined). Ideally, he would like to continue like 3.Nf3 Nf6 4.e3 Bf5 (or ...Bg4), followed by completing the development of the kingside. In the mainline of the Slav Defence 3.Nf3 Nf6 4.Nc3 Black plays 4...dxc4 (the immediate 4...Bf5? is a mistake due to 5.cxd5 cxd5 6.Qb3! when Black’s best move is the sad 6...Bc8) 5.a4 Bf5, again achieving the objective.
Starting position of the Slav Defence Mainline
Playing ...dxc4 followed by ...b5 can be connected to developing the queen’s bishop to b7, aiming to open the long diagonal with ...c5. For example 3.Nf3 Nf6 4.Nc3 e6 5.e3 Nbd7 6.Bd3 dxc4 7.Bxc4 b5 8.Bd3. The Meran Variation, is the starting point of many sharp lines. We have a look at one to demonstrate some important ideas. 8...Bb7 9.e4 b4. After White has taken the center, Black wants to prepare his counterplay as quickly as possible. With ...b4 he kicks the white knight to the edge of the board and is ready to play ...c5 on the next move. 10.Na4 c5 11.e5 Nd5.
A typical position from the Meran Variation
White has advanced aggressively in the center and will try to use his advantage in development to start an attack, while Black has activated his light-squared bishop and was granted a beautiful knight on d5. The sharp pawn sacrifice 12.0-0 cxd4 13.Nxd4 Nxe5 14.Bb5+ Nd7 15.Re1 leads to a typical scenario. Black has a good position if he once he manages to complete his development, while White will go all out to decide the game with an attack.
The first player has several gambit lines at his disposal. E.g. the Geller Gambit 3.Nf3 Nf6 4.Nc3 dxc4 5.e4 b5, the Botvinnik Variation 4.Nc3 e6 5.Bg5 dxc4 6.e4 b5, and the Anti-Moscow Gambit 5...h6 6.Bh4 dxc4 7.e4 g5 8.Bg3 b5.
Starting position of the Anti-Moscow Gambit
We can see a typical situation in the diagram. Black has firmly defended the c4-pawn, but had to make some concessions. His kingside is weakened and White has a strong pawn center. Such unbalanced and sharp positions offer both sides good chances to play for a win.
In lines where Black develops his bishop to f5 or g4, he is often ready to give up the light-squared bishop for the f3-knight. Most commonly this scenario happens in the 3.Nf3 Nf6 4.e3 line. E.g. 4...Bf5 5.Nc3 e6 6.Nh4 Be4 (provoking f3; 6...Bg6 is also possible) 7.f3 Bg6 8.Bd2 Be7 9.Nxg6 hxg6.
White has "won" the pair of bishops, while Black keeps a solid position. Note that Black’s pawns in the center are on white squares, which helps to restrict the f1-bishop. The position seems quiet, but can sharpen up quite a bit as White is going to castle queenside. 10.Qc2 Nbd7 11.0-0-0. White is ready to play in the center or to answer 11...0-0?! with 12.h4. Black does best to start some direct counterplay with 11...dxc4 12.Bxc4 b5 or the preliminary 11...a6 followed by ...dxc4, ...b5, and ...c5.
In a way, both sides can be happy in these types of positions. Black had to part with the light-squared bishop, but his position remains solid with some potential for counterplay. White on the other hand, hopes that the pair of bishops shows its potential in the long run.
White goes for a symmetrical pawn structure (where his only advantage lies in his extra tempo) and prevents any counterplay based on …dxc4 and …b5. Once having had peaceful reputation, new ways found to induce some imbalance into the position.
3.cxd5 cxd5 4.Bf4 (beginning with 3.Nc3 allows the extra options 3…e5 and 3…Nc6 4.Bf4 e5!?) 4…Nf6 5.e3 Nc6 (5…Qb6 might be investigated to mix things up) 6.Nc3. 6.Bb5!? from Caruana-Duda, Norway Chess 2020, has been seen in some high-level games since this encounter. The possibility of saddling Black with a backward c-pawn gives the game an independent character. 6…Bf5 7.Qb3!?. This is the modern way of playing this line. In the ‘old’ continuation 7.Nf3 e6 8.Bb5 Nd7 the way for Black to equalize has been worked out to near perfection. After 7.Qb3 Na5 8.Qa4+ Bd7 9.Qc2 e6 10.Bd3 Rc8 11.Nf3 Bb4 12.0-0 0-0 the following position arises.
The strange dance of the white queen and black bishop has led to an original position. Black has counter chances on the c-file, whereas his light-squared bishop has been lured to a passive position and the a5-knight is on the rim, making Ne5 a good option for White. Due to these imbalances the position is anything but boring – both sides have their chances!
Black’s most popular continuation on move six is the "mysterious" 6…a6!?. Black makes a useful move, hoping for 7.Nf3 Bg4!. White has several options to deny Black this possibility, for instance 7.Rc1 Bf5, when White can argue that his rook-move is more useful than moving the rook-pawn. On the other hand Black has neutralized the idea 8.Qb3 Na5 9.Qa4+ as it can now be answered by 9…b5. A different line to combat the 6…a6-idea is to play 6.Nf3 (instead of 6.e3) to answer 6…a6 with 7.Ne5!?, with the idea of saddling Black with a backward c-pawn.
In order to get a good understanding of the Exchange Variation it is useful to study the games of the biggest specialists, e.g. Alexander Rakhmanov for White and Alexey Dreev for Black.
4.e3 has become one of the most important lines in the whole Slav complex and is IM Kushager Krishatner’s recommendation in his Top-Level Repertoire against the Slav Defence. White’s strategy is quite straightforward: if Black develops his light-squared bishop to f5 or g4, he will aim to gain the pair of bishops. If Black develops with 4…e6 or 4…g6 (the Schlechter Variation), White often reaches a slightly better position due to his space advantage. Lines like 4…Bf5 5.Nc3 e6 6.Nh4 or 4…Bg4 5.Nc3 e6 6.h3 Bxf3 (if Black plays 6…Bh5, White can play 7.g4 Bg6 8.Ne5) 7.Qxf3 are very popular. After acquiring a basic understanding of the most important plans, they can be played with both colors without having to study loads of theory (see also above, “Basic Concepts – White goes for the Pair of Bishops”).
A fresh example from tournament practice shows, that after a quiet start, matters can quickly heat up:
Position after 13…b5, Ter Sahakyan-Shirov, Douglas 2023
White unleashed the piece sacrifice 14.Bxe6 fxe6 15.e5 Nd5 16.Nxd5 cxd5 17.Qxg6+ with excellent compensation. Ter Sahakyan later won a good game against Alexei Shirov, a great connoisseur of the Slav Defence.
Quite an interesting and challenging line in respect to the different types of positions it can lead to. 4.g3 g6 is a Fianchetto Grünfeld, while 4…e6 leads to the Catalan. Taking the pawn with 4…dxc4 leads to sharp play, with likely transpositions, e.g. 5.Bg2 b5 (or 5…g6; again a Fianchetto Grünfeld) 6.0-0 Bb7 7.b3!? cxb3 8.Qxb3 e6, again reaching a Catalan.
With 4…Bf5 and 4…Bg4 Black can stay on Slav territory. After 4…Bf5 5.Nc3 e6 going after the f5-bishop with 6.Nh4 is White’s main try, with similar ideas to 4.e3 Bf5 5.Nc3 e6 6.Nh4. 4…Bg4 5.Ne5 Bf5 leads to a different kind of game. A fairly recent idea is 6.cxd5 cxd5 7.Nc3 Nc6 8.f3!?.
White fights for space and tries to prove that the position of the f5-bishop is problematic. This and other topical lines of the 4.g3-complex are investigated by GM Michael Roiz in his two-part course Expert Repertoire against the Slav Defence - Part 1 and Part 2.
4.Qc2 and 4.Qb3 are solid and playable moves that are analyzed by GM Aleksander Delchev in his Positional Repertoire against the Slav Defence. White keeps the options of developing the c1-bishop to g5 or f4 before playing e3 and to Fianchetto the f1-bishop. If Black answers with the common 4…dxc4, both moves lead to the same position. 5.Qxc4 Bf5 6.g3, is a solid line where White’s extra pawn in the center gives him modest chances for an advantage. Black can vary with 4.Qc2 g6!? and 4.Qb3 e6, when both moves show certain drawbacks of the early queen moves. The queen on c2 does not feel to well after …g6 (…Bf5 will at some point win a tempo), whereas Qb3 isn’t usually played in the Queen’s Gambit Declined.
4.Nbd2 looks quite harmless, and it is too! Just don’t fall for 4…Bf5 5.Nh4 Bg6?! (5…Be4 is fine for Black) 6.Qb3 Qb6?! 7.Qh3!.
Black is in some trouble as he faces the unpleasant threats of Qc8+ and Nxg6, when he is forced to take back with the f-pawn.
This continuation was developed by the renowned trainer and theoretician Vyacheslav Chebanenko (1942-1997) and became popular in the 1990s. How can this little move with the rook-pawn be justified? Black would like to develop his bishop to f5 or g4, but he can’t do so immediately due to 4…Bf5?! 5.cxd5 cxd5 6.Qb3!, when Black has to make a concession to defend b7. In the Classical Slav Black gives up the center with 4…dxc4 to be able to play …Bf5, while in the Semi-Slav Black abandons this idea altogether by playing 4…e6. So how does 4…a6 help to prepare the development of the c8-bishop? For instance after 4…a6 5.e3 b5 6.b3 Bg4 White no longer has Qb3, while another more original idea is 4…a6 5.e3 Bf5 6.Qb3 Ra7!?.
White has several ways to combat the Chebanenko; e.g.: 5.c5 looks very logical as White fixes the weakness on b6. On the downside he loses some flexibility and Black has the logical plan of preparing counterplay with …e7-e5. After 5.a4 Black usually plays 5…e6 leading to a sort of Semi-Slav with the extra moves a4 and …a6, which in some cases helps Black, as the square b4 is weakened. The most solid continuation is 5.e3. A sample line runs: 5…b5 6.b3 Bg4 7.Be2 e6 8.h3 Bh5 9.0-0 Nbd7 10.Bb2 Bd6 11.Ne5 Qxe2 12.Nxe2 Qc7 13.cxd5 cxd5 14.Rc1 Qb8 15.Nxd7 Nxd7.
Now White can achieve a slight initiative with the energetic 16.e4! dxe4 17.d5!, when after 17…0-0 Black has enough resources to gradually equalize.
All in all Chebanenko’s idea has been proven viable in theory and practice and can be regarded as an original and solid alternative to the Classical Slav and the Semi-Slav.
Now 5.a4 Bf5 is the main continuation by far. Harmless is 5.e3 b5 6.a4 b4 7.Na2 (other knight moves don’t change the assessment) 7…e6 8.Bxc4 Bb7. White loses too much time with his knight, while Black will carry out …c5, achieving a good game. The continuation 5.g3 can lead to quite sharp play and likely leads to the Catalan Opening. The Geller Gambit 5.e4 has been played quite a lot recently in events with faster time controls. After 5…b5 a new trend is to go for 6.Be2 or 6.Qc2 relying on White’s positional compensation for the pawn, in favor of the ‘old’ 6.e5 which leads to more concrete play. White gets reasonable play and Black definitely should be prepared for this.
This is a fully viable alternative to 5…Bf5. One of Black’s ideas comes to the fore after 5…e6 6.e3 c5 7.Bxc4 cxd4 8.exd4 Nc6 9.0-0 Be7.
We have reached a position from the Queen’s Gambit Accepted with the extra move a2-a4 for White, which gives Black an improved version as the square b4 is weak. White has the usual play, typical of positions with the isolated d-pawn, but would like to rather have his pawn on a3.
White can be more ambitious with the pawn sacrifice 6.e4 Bb4 7.Bg5 (7.Bxc4 Nxe4 8.0-0 is interesting, but probably not fully sound if Black finds the strongest move 8…Nf6) which leads to the line 6.a4 of the Botvinnik Variation. Both sides need to show good preparation when going for this.
6.Nh4 is much less played than 6.e3 or 6.Ne5, but actually scores better statistically (roughly 62%)! Black has several playable options of how to deal with the knight move. Combative and playable is 6…e6 7.Nxf5 exf5 8.e3 Bb4 9.Bxc4 0-0 (this position can also arise from 6.e3). As compensation for White’s pair of bishops, Black has free development and good central control – the doubled pawn on f5 forms a nice outpost on e4. In a lot of games 6…Bc8 was played, challenging White to justify his knight-move. This can lead to an IQP-position after 7.e3 e5!? 8.Bxc4 exd4 9.exd4. A line rated highly by the engines is 6…Bd7 7.e4 (the most ambitious move) 7…e6 8.Bxc4 Nxe4 9.Nxe4 Qxh4 10.Qf3 Bb4+ 11.Kf1.
Black has won a pawn but has his pieces in strange positions. Despite Stockfish showing triple zeros, White scored 68% (out of 64 games in total)! Apparently this position is not easy to play… The conclusion suggest itself, that 6.Nh4 can be quite a good (surprise-)weapon and Black does best to take it seriously.
White goes for rapid development and will later decide on a concrete plan. 6…e6 7.Bxc4 Bb4 8.0-0. Now Black can castle or play the preliminary 8…Nbd7, when preparing e3-e4 with 9.Qe2 is White’s most important idea. After 9…Bg6 White plays 10.e4! anyway.
Now taking the central pawn with 10…Bxc3?! 10.bxc3 Nxe4 is ill-advised due to 11.Ba3!, with more than enough compensation. Instead, the main line runs 10…0-0 11.Bd3 Bh5 (with the idea 12…e5) 12.e5 Nd5 13.Nxd5 cxd5. A typical scenario in the Slav: White has more space, while Black has the customary solid position. White mainly played 14.Qe3 with the idea of moving the knight and then to go forward with the f-pawn.
Since in the above line White’s play is a bit easier, the trend has shifted to 8…0-0 which effectively neutralizes the idea from above: 9.Qe2 Bg6. Now 10.e4? Bxc3 11.bxc3 Nxe4 is no longer good as Black can safely take the pawn - his king is already castled. On the other hand 10.Ne5 is possible. 10…Nbd7 11.Nxg6 hxg6, with another familiar picture:
White has the pair of bishops, while Black has a healthy position, e.g. 12.Rd1 Qa5 13.e4 e5, with about equal chances.
This is White’s most ambitious choice. 6.Ne5 serves to prepare f3 followed by e4, not only building a strong pawn center, but also kicking away the f5-bishop. Apart from some lesser alternatives, Black has three important lines to combat this system.
A) 6…e6 7.f3 Bb4
Black develops in the most active manner and is prepared to sacrifice a piece: 8.e4 Bxe4! (forced to some extend, as otherwise Black’s opening would be a failure) 9.fxe4 Nxe4 10.Bd2 Qxd4 11.Nxe4 Qxe4+ 12.Qe2 Bxd2+ 13.Kxd2 Qd5+ 14.Kc2.
After the most common continuation 14…Na6 15.Nxc4 0-0 16.Qe5 Rab8 chances are about equal, with White having a slight plus-score in practice. Another (quite modern) way for White to play is: 8.Nxc4 0-0 9.Kf2!?. In Ding-Caruana, Candidates tournament 2020, the latter uncorked 9…e5!?, which led to a complex struggle with chances for both sides. These lines seem attractive enough, but for some reason 6…e6 is not seen too often in practice. Possibly players with the black pieces don’t like the forcing character of the play or are reluctant to study the vast amount of theory connected to those lines.
B) 6…Nbd7 7.Nxc4 Qc7
Black prepares the advance of his e-pawn. After 8.g3! e5 9.dxe5 Nxe5 10.Bf4 Nfd7 11.Bg2 the stunning 11…g5!?, from the stem game Kasparov-Morozevich, Wijk aan Zee 2000, is still the most popular move.
Following 12.Ne3 gxf4 13.Nxf5 0-0-0 an unbalanced situation arises that has been tested extensively in practice. White has the more compact pawn structure, while Black has good piece play.
C) 6…Nbd7 7.Nxc4 Nb6 8.Ne5 a5
Black defends against a4-a5 and fixes the weak square on b4. This line is somewhat less forcing than variations A) and B), though some basic ideas need to be memorized. White will try to make something of his space advantage, while Black aims complete his development and strike at White’s center with …e5 or …c5. We will look at one of the most principled lines (White has tried every sensible continuation on move nine) to see what direction the game can take: 9.f3 Nfd7! 10.e4 Nxe5 11.exf5 Ned7 12.d5 g6!.
After 13.dxc6 bxc6 14.Qd4 Rg8! is an important resource for Black, with the idea 15.fxg6 Rxg6!?, developing the rook in an original way! White can play more quietly with 10.Nxd7 Nxd7 (or 10…Bxd7), when after the exchange of one pair of minor pieces, White’s space advantage isn’t too much of an issue any more – Black retains good equalizing chances.
Why play …e6 after …c6 in the first place? Well, White has to think twice before opting for ‘normal’ developing moves, as Black can take on c4 and defend the pawn with …b5, leading to sharp play. Going for the Exchange Variation of the QGD is no longer that promising, as White’s knight is already on f3, e.g. 5.cxd5 exd5 6.Bg5 h6 7.Bh4 Bf5 is fine for Black. 5.g3 with a transposition to the Catalan (with the unusual Nc3 included), might turn out to be a gambit, as White must be prepared to sacrifice the c4-pawn. The most important continuations, 5.e3 and 5.Bg5, will be dealt with in more detail below. In the former White defends c4, agreeing to shut in the c1-bishop, in the latter White is prepared to enter a bunch of complex lines as Black can go for …dxc4.
The principled continuation is 6…dxc4 7.Bxc4 b5 8.Bd3 (other bishop moves are less critical). The position bears some structural resemblance to the Queen’s Gambit Accepted. Here however, White’s knight is already on c3 which takes the sting out of plans involving a4, as …b4 hits the c3-knight. On the other hand, Black hasn’t played …c5 yet, and that gives White the possibility of a quick e4.
Now Black has a choice of two quite solid lines 8…b4 9.Ne4 Nxe4 10.Bxe4 Bb7 and 8….Bd6. In the first one Black will follow up with …Be7 and …0-0 and then go about patiently preparing …c5, when he gradually will equalize. In the second one Black takes the sting out of e4, by having …e5 ready.
The sharper alternatives are 8…Bb7 and 8…a6, when the plans of both sides clash immediately: White advances in the center and Black goes carries out …c5. 8…Bb7 9.e4 (9.0-0 a6 likely transposes to 8…a6) 9…b4 10.Na4 c5 11.e5 Nd5 leads to a sharp battle – White is better developed and has attacking chances, while Black has made some positional gains (strong b7-bishop and knight on d5). 8…a6 9.e4 c5 offers White two sharp attacking continuations, 10.d5 and 10.e5. The latter played a decisive role in the World Championship match Anand-Kramnik, Bonn 2008. Anand won two consecutive games as Black in the following sharp line: 10.e5 cxd4 11.Nxb5 axb5 12.exf6 gxf6 13.0-0 Qb6 14.Qe2.
In both games the pawn sacrifice 14…Bb7!? was played. Anand’s cunning preparation paid off and he managed to score two wins from unclear positions against his formidable opponent.
With 6.Qc2 White is reluctant to waste a tempo by moving the f1-bishop yet. Following 6…Bd6 (6…b6 is a playable alternative) the play can take very different directions. White can venture the Shirov-Shabalov Attack with 7.g4!? or play in the center with 7.e4. More solid lines are 7.b3 and the most popular continuations 7.Be2 and 7.Bd3 (both can lead to the same position if Black takes on c4). Let’s have a look at an important line: 7.Bd3 0-0 8.0-0 dxc4 (8…e5!?, 8…Re8!?) 9.Bxc4 b5 10.Bd3 (10.Be2 is the other main move) 10…Bb7 11.a3 Rc8!? 12.b4 c5!!.
In these lines it is vital for Black to push …c5 and in the above position he manages to do it in the most spectacular way! The tactical point lies in 13.bxc5 Bxf3 14.gxf3 Nxc5! 15.d
In these lines it is vital for Black to push …c5 and in the above position he manages to do it in the most spectacular way! The tactical point lies in 13.bxc5 Bxf3 14.gxf3 Nxc5! 15.dxc5 Rxc5 when due to the threats 16…Bxh2+ (leading to a draw) and winning the c3-knight Black regains his material, e.g. 16.f4 Nd5 17.Bb2 Nxc3 18.Bxc3 Qc7 19.Rfc1 Rc8, with equality.
With 5…dxc4 Black forces White to play as sharply as possible, since he is ready to defend the c4-pawn with …b5. 6.e4 (6.a4!? Bb4 7.e4 can be an interesting alternative) 6…b5 7.e5 h6 8.Bh4 g5 9.Nxg5 hxg5 10.Bxg5.
We have reached the basic tabia of the Botvinnik Variation. We’ll have a look at it in more detail in our sample game Polugaevsky-Torre.
Here we enter much quieter waters. White relinquishes his dark-squared bishop in exchange for swift development and a space advantage. Black’s position may look a bit cramped, though the pair of bishops offers chances for a potential counterplay once the position opens up. A typical example: 7.e3 g6 (g7 is the best place for the black-squared bishop) 8.Bd3 Bg7 9.0-0 0-0 10.e4 (the most principled move) 10…Qd8!? (keeping the tension) with the idea 11.e5 c5!?.
Black manages to open the position and gains adequate counter chances.
As opposed to the Botvinnik Variation White offers a real gambit. After 7.e4 g5 8.Bg3 b5 9.e4, we have reached the starting position of this line. White has excellent compensation for the sacrificed pawn due to his strong pawn center and the opponent’s weakened king position. If well prepared, Black gets his fair share of chances in the complications. Sometimes he even manages to use his kingside pawns for a counterattack:
This position was reached in the analysis of the game Aronian-Anand, Mexico City 2007. Black wins by a pointed series of moves: 20…g3! 21.Be3 Qd8!. Suddenly White’s king is the more vulnerable one. 22.Bg5 Bxd4+ 23.Rxd4 Qb6! 24.Be3 e5!, winning material as 25.Rd3 doesn’t help due to 25…cxd3!.
This move order can lead to the lines discussed above, but contains some move order subtleties. After 3…Nf6 (3…dxc4 and the Winawer Gambit 3…e5 are sharp alternatives) 4.e3 e6 5.Nf3 White transposes to the Meran or Anti-Meran lines, while having avoided the Mainline Slav. Can’t Black just play 4…Bf5? Well, compared to the line 3.Nf3 Nf6 4.e3 Bf5, White’s c3-knight puts d5 under pressure, which makes a difference. Following 4…Bf5 5.cxd5 cxd5 6.Qb3 Black only can defend the b7-pawn with the unattractive 6…Bc8 (6…b6? represents too much of a weakening). This led 4…Bf5 to be discarded by most players, until the pawn sacrifice 6…Nc6!? was found. Practice has shown that after 7.Qxb7 Bd7 8.Qb3 Rb8 9.Qd1 e5 10.dxe5 Nxe5 11.Be2 Bd6 12.Nf3 Nxf3+ 13.Bxf3 Qc7!, Black has full compensation.
White has to spend a tempo to be able to castle. 14.h3 0-0 15.0-0 Rfd8 and Black’s advantage in development offsets White’s extra pawn – the position is theoretically about equal, while the practical results favor Black.
We haven’t yet mentioned the possibility of 3.Nc3 e6 or 3.Nf3 e6 – i.e. the Triangle System. Please have a look at the article on the Queen's Gambit Declined for more information on this. When going for the Triangle System many players go for 2…e6 and play …c6 only afterwards to avoid the symmetrical structure of the Slav Exchange Variation.
Concerning some move order subtleties: Black might go for the Chebanenko only once e3 has been played, to reduce White’s options. 3.Nf3 Nf6 4.e3 a6!? and 3.Nf3 Nf6 4.Nc3 e6 5.e3 a6!? are lines one should be aware of. The latter was Anand’s main defence with Black in his World Championship match against Gelfand.in 2012.
Together with the Queen’s Gambit Declined and the King’s Indian Defence, the Slav Defence can be used as a universal weapon against all closed openings. There’s of course some independent theory to be studied after 1.Nf3 and 1.c4, but the basic setup ...d5 (against 1.c4 Black starts with ...c6), ...c6, ...Nf6, followed by developing the light-squared bishop works in most cases. Check out GM Alvar Alonso’s Repertoire against the Reti Opening, King's Indian Attack, and English Opening, (optimized for Slav Defence aficionados) and the camp database Slav Setups against the English, Reti and Larsen.
To get a better all-round understanding of the various lines after 1.d4 (e.g. how to create winning chances as Black in the Exchange Variation, neutralizing White’s pair of bishops, etc.) there’s Understand the Slav Defence.
Usually players who like a sharp fight and are not averse to serious preparation go for the Semi-Slav. People, who don’t fancy the Exchange Slav or the 3.Nf3 Nf6 4.e3-line, can get to it via the move order 1.d4 Nf6 2.c4 e6 3.Nf3 d5 4.Nc3 c6 – bingo. However then there’s the Nimzo-Indian and Catalan to be learned.
We have two Semi-Slav courses for Black on modern-chess.com. GM Ivan Cheparinov’s Semi-Slav Defence - Top Level Repertoire for Black and GM Renato Quintiliano’s three-part series Semi-Slav - Complete Repertoire for Black, Semi-Slav - Complete Repertoire for Black - Part 2, and Play the Moscow Variation. Both courses offer different repertoire suggestions in practically all the main lines and complement each other perfectly.
The Classical Slav suits players of a solid positional style. Black’s mode of development is both straightforward and healthy. I guess this makes it a reasonable choice for beginner and expert alike. GM Renato Quintiliano published an extensive three-part course with Solid Repertoire against 1.d4 - Slav Defence - Part 1, Part 2, and Part 3.
The Chebanenko Variation is also quite solid character, while the concepts behind it are already quite sophisticated. So: probably not the ideal line for beginners, but a good choice for experienced club players. There’s some theory to master, though less than in the Classical Slav or the Semi-Slav.
I have made a brief overview of possible ways to go.
1 – Playing the Exchange Variation
Pros: drastically restricts Black’s options, easily understandable plans
Cons: fixed pawn structure reduces dynamic possibilities
2 – Playing the 3.Nf3 Nf6 4.e3-line
Pros: manageable theoretical effort necessary, good theoretical weapon for positional players
Cons: Black has various ‘solid’ lines available
(see IM Krushatner’s repertoire in “Main- and Sublines”)
3 – Playing the 3.Nf3 Nf6 4.g3-line
Pros: good theoretical weapon, leading to an interesting variety of positions
Cons: challenging in respect to the different types of postions it can lead to
(see GM Roiz’ repertoire in “Main- and Sublines”)
4 – Playing 3.Nf3 Nf6 4.Nc3 dxc4 5.a4 Bf5 6.e3 and 4…e6 5.e3
Pros: a good mix of aggression and solidity, leads to positions rich in content
Cons: solid preparation and good understanding required
5 – Playing 3.Nf3 Nf6 4.Nc3 dxc4 5.a4 Bf5 6.Ne5 and 4…e6 5.Bg5
Pros: aggressive opening play can lead to a serious advantage, positions with many dynamic and attacking possibilities
Cons: very serious preparation required
GM Davorin Kuljasev published a three-part course for White: GM Repertoire against the Slav, Part 2, and Part 3, combining variations from point 4 and 5 above to offer an ambitious repertoire.