The Caro–Kann defence is a chess opening. It is a defence for Black when White opens by moving his King's pawn two squares on the first move. It begins: 
1.e4 c6
Usually, the next moves are:
2.d4 d5 
It is then followed by 3.Nc3 (the Modern Variation), 3.Nd2 (the Classical Variation), 3.exd5 (the Exchange Variation), or 3.e5 (the Advance Variation). The modern variation (3.Nc3) is most popular. 

The Caro–Kann, like the Sicilian defence and French defence, is an asymmetrical defence to 1.e4. These are sometimes called 'semi-open games'. The Caro is thought to be more solid and less dynamic than the others, which means that play is likely to be more quiet and positional. It may lead to good endgames for Black, who has the better pawn structure.

The opening is named after the English player Horatio Caro and the Austrian Marcus Kann, who studied the opening in 1886.

Classical or Capablanca variation 
The most common way of handling the Caro–Kann, the Classical variation (often called the Capablanca variation) happens after the moves 
1.e4 c6
2.d4 d5
3.Nc3 (or 3.Nd2) dxe4
4.Nxe4 Bf5
For a long time, this was thought to be the best play for both sides in the Caro–Kann. White usually continues
5.Ng3 Bg6
6.h4 h6
7.Nf3 Nd7
8.h5 Bh7
9.Bd3 Bxd3
10.Qxd3
Although White's pawn on h5 looks ready to attack, it can prove to be a weakness in an endgame.

This variation is a big reason that people think the Caro-Kann is a solid defence. Black makes very few compromises in his pawn structure, and plays c5 in time to fight for the d4 square. Black can castle queenside, castle kingside, or even leave his king in the centre. Should the game go to an endgame, Black often has good chances because of his solid pawn structure and kingside pawn majority.

Smyslov or Modern variation 
Another solid positional line is the Modern variation. It happens after the moves 
1.e4 c6
2.d4 d5
3.Nc3 (or 3.Nd2) dxe4
4.Nxe4 Nd7
Played by the first world champion Wilhelm Steinitz, today the variation is called either the Smyslov variation or, most often, the Modern variation. 

The short-term goal of 4...Nd7 is to make developing his pieces easier by trading a pair of knights without damaging his pawn structure by the direct 4...Nf6. Play is similar to the Classical variation except that Black is not forced to play his QB to the g6 square. However, this freedom comes at a cost as White is able to take up space in the center. White often plays the aggressive 5.Ng5!? pressuring key points such as the f7-square.

This variation can lead to a quick mating trap with 5.Qe2 Ngf6?? 6.Nd6#.

4...Nf6 variations 
Two variations begin with:
1.e4 c6
2.d4 d5
3.Nc3 dxe4
4.Nxe4 Nf6!?
5.Nxf6+ 

The Bronstein–Larsen Variation is after:
5...gxf6!?
Black has chosen a worse pawn structure, and often castles queenside. Black does have compensation, with the open g-file for the rook and unusually active play for the Caro-Kann. It is generally considered somewhat double-edged.

The Korchnoi Variation arises after:
5...exf6
Viktor Korchnoi has played 5...exf6 many times (including his first world championship match with Anatoly Karpov), and this line has also been employed by Ulf Andersson. Black's 5...exf6 is thought to be sounder than 5...gxf6!? of the previous and offers Black fast development, though also giving White the superior pawn structure and long-term prospects.

Advance variation 
The Advance variation is 3.e5:
1.e4 c6
2.d4 d5
3.e5 

The main replies are:

3...Bf5
is most often played. Against it are aggressive lines such as the Bayonet Attack (4.Nc3 e6 5.g4), a popular line in the 1980s and later favoured by Latvian Grandmaster Alexei Shirov. A more natural development 4.Nf3 e6 5.Be2 c5 6.Be3 was popularised by English Grandmaster Nigel Short and often seen in the 1990s.

3...c5 is an important alternative which avoids the opening theory on 3...Bf5. It was used by Botvinnik in his 1961 match with Tal. In comparison to the French defense, Black gains the tempo normally spent on ...e6. However, White can counter this by opening the centre with 4. dxc5. This exposes the black pawn on d5.

3...e6 is natural and playable, but when Black plays ...c5 (as he soon will do) he is a tempo behind the advance line of the French defence (1e4 e6 2.d5 d5 3.e5 c5).

Exchange variation and Panov-Botvinnik Attack 
The Exchange Variation is
1.e4 c6
2.d4 d5
3.exd5 cxd5.
The Panov-Botvinnik Attack begins with the move
4.c4.

This system often leads to typical isolated queen's pawn (IQP) positions, with White gaining rapid development, a grip on e5, and kingside attacking chances to make up for the long-term structural weakness of the isolated d4 pawn. The major variation in this line 4...Nf6 5.Nc3 e6 6.Nf3, when Black's main alternatives are 6...Bb4 (a position which often transposes into lines of the Nimzo-Indian defence) and 6...Be7, once the most common line. 6...Nc6?! is inferior as it is favourably met by 7.c5!, after which White plans on seizing the e5-square through the advance of his b-pawn to b5 or by exchanging the Black's Knight on c6 after Bb5.

The "true" Exchange Variation begins with
4.Bd3 Nc6
5.c3 Nf6
6.Bf4 Bg4
7.Qb3
This line is thought to have equal chances for both sides, and was tried by Bobby Fischer. Some of the strategic ideas are analogous to the Queen's Gambit declined, Exchange variation, (1.d4 d5 2.c4 e6 3.Nc3 Nf6 4.cxd5 exd5) with colours reversed.

Two knights variation 
This is  1.e4 c6 2.Nf3 d5 3.Nc3, played by Bobby Fischer in his youth. White gets rapid development and has options with the d-pawn. Black's logical and probably best reply is 3...Bg4. After 4.h3 Bxf3 5.Qxf3, the positional continuation, Black has the option of 5...Nf6 or 5...e6. 4....Bh5 is a complicated line, in which White can trap the bishop, though Black has much compensation.

The variation sets a trap: if Black plays along the lines of the Classical Variation, he gets in trouble after 3...dxe4 4.Nxe4 Bf5 (4...Nd7 is playable) 5.Ng3 Bg6?! (5...Bg4) 6.h4 h6 7.Ne5 Bh7 (7...Qd6 may be best) 8.Qh5! g6 (forced) 9.Bc4! e6 (9...gxh5?? 10.Bxf7#) 10.Qe2 with a huge advantage for White. Now 10...Qe7! is best. Instead, Lasker–Radsheer, 1908 and Alekhine-Bruce, 1938 ended quickly after, respectively, 10...Bg7?? 11.Nxf7! and 10...Nf6?? 11.Nxf7!

Other lines 
White can play 2.c4. Then Black may play 2...d5 (see 1.e4 c6 2.c4 d5). This can transpose to the Panov–Botvinnik line given above, with 3.exd5 cxd5 4.d4 or White can capture twice on d5. Alternatively, Black may play 2...e5.

Also, White can play 2.Nc3. Then Black may play 2...d5. If White replies 3.d4 then we get the main Capablanca line or the Two knights variation. Or Black may play 2...g6.

The Caro–Kann can also be reached through the English Opening: 1.c4 c6 2.e4 d5.

ECO codes 
The Encyclopaedia of Chess Openings has ten codes for the Caro–Kann Defence, B10 to B19.

Related pages
 List of chess openings

More reading

 
 Martin, Andrew 2007. The ABC of the Caro Kann. ChessBase Publications. Fritz Trainer DVD.
 

Also, more advanced:

References

Chess openings