The Semi-Slav has a reputation for solidity, but at the same time it leads to a lot of sharp positions. The sharpest positions arise out of the Botvinnik variation, which comes after White plays 5.Bg5 (1.d4 d5 2. c4 c6 3. Nf3 Nf6 4. Nc3 e6 5. Bg5) and then Black immediately plays 5...dxc4. As for sharpness and complexity, the positions are about a 9.5 on a scale of 10. Next comes the Anti-Moscow Gambit. Instead of 5...dxc4 (as in the Botvinnik), Black plays h6, and White, then instead of 6.Bxf6 (the Moscow variation), plays the bishop back to h4. The variation usually continues 6...dxc4 7.e4 g5 8.Bg3 b5. These positions are only slightly less sharp than the Botvinnik (noting that the Anti-Moscow can lead to the Botvinnik). Sharpness isn't limited to the Bg5 variations of the Semi-Slav.
Should White play e3 before developing the dark-squared bishop, the most likely positions arising are those of the Meran. The opening's name comes from Merano, Italy, where a significant international tournament was held in 1924. Gruenfeld won the tournament winning 9, drawing 3, and losing 1. His lone loss was with the white pieces to Rubinstein, who, right, played the Meran. Gruenfeld then turned around and played the Meran against Rudolf Spielmann, handing him one of only two losses suffered in the tournament. Gruenfeld, Spielmann, and Rubinstein finished 1, 2, 3. Despite the opening's name, there are at least 6 earlier instances involving the "Meran," going back to 1906, and involving such names as Schlechter, Capablanca, and Euwe.
The Meran begins 1.d4 d5 2.c4 c6 3.Nf3 Nf6 4.Nc3 e6 5.e3 Nbd7 6.Bd3 dxc4 7.Bxc4 b5 8.Bd3 Note that an early theme of the Meran is that of achieving a gain of tempo on the dxc4 exchange. Black almost always waits for the light-squared bishop to move before initiating the exchange.
Now we reach a critical crossroads. The current Meran fashion calls for 8...Bb7. This is the only move considered by Vigorito in Play the Semi-Slav, which is fair in a repertoire book. The other move, which has enjoyed a mild resurgence due to Anand's playing it against Kramnik in the 2008 W.Ch., is 8...a6. Glenn Flear, in starting out: slav and semi-slav, refers to 8...a6 as the Old Meran. In The Meran Semi-Slav, Reinaldo Vera calls this the Classical Meran, a name I prefer since it says a little less about the future status of the opening. And Mathew Sadler, in The Semi-Slav, calls it the Old Main Line, which is accurate at least at present. In any event, after 8...a6, White plays one of three moves: 9.e4, far and away the most popular, 9.O-O, which has not served White well statistically, and 9.a4, which will deserve a closer look later. In the below games, we'll focus on 9.e4. Black will reply quickly with 9...c5 (alternatives being 9...b4 and 9...Bb7, which are simply too slow and have not scored well). Now White has two moves: 10.e5 and 10.d5, both of which are viable. We'll come back to d5 later.
This game illustrates some of the hazards of White not getting his king tucked away.