Chess Opening Theory/1. e4/1...c6/2. d4/2...d5/3. e5

3. e5 closes the centre and gains space. This is one of the most popular and serious lines against the Caro-Kann.

Black has two main responses: 3...Bf5 and 3...c5.

A common idea is to achieve a pawn break with ...c5, attacking the base of White's pawn chain. However, If ...c5 there is a possibility of dxc5, and if so Black would ideally to recapture while developing their bishop. That requires moving the e-pawn, however.

Therefore, 3...Bf5 is the main line. Black develops their light-square bishop, so that they may freely play ...e6, so that the dark-square bishop may support ...c5. Black achieves an improved version of the advanced French, having developed with their bishop outside of the pawn chain.

The main continuations are the patient Short variation, 4. Nf3 e6 5. Be2, and the sharp van der Wiel or Shirov attack, 4. Nc3 e6 5. g4.

3...c5 immediately, the Botvinnik-Carls defence, is an important sideline. 3...c5 attacks the base of White's pawn chain and threatens to undermine their centre. 3...c5 encourages 4. dxc5, weakening the pawn on e5. Black can usually recover the pawn, though has a harder time developing their light-squared bishop (4...Nc6 (attacks e5) 5. f4 e6 (discovered attack on c5) 6. Be3 d4! 7. Bf2 Bxc5). 4. Nf3 cxd4 5. Nxd4 is also played.

In principle it should be wrong for Black to move their c-pawn twice in the opening, and this is a disadvantage of the Caro-Kann compared to the French, but as White also moved a pawn twice, Black doesn't fall behind.

Minor alternatives include 3...g6, which prepares ...Bg7 and suggests the possibility of avoiding e6 and playing an f6 pawn break;^[1] 3...Na6!?, preparing ...Nc7; and 3...Qb6?!.

3. e5 was regarded as inferior for a long time, owing chiefly to the strategic demolition that Aron Nimzowitsch with the white pieces suffered at the hands of Jose Capablanca in 1927.^[2] However, it has been revitalised with lines ranging from positional manoeuvring to aggressive and tactical: today it is the main line in tournament chess.

1.e4 c6 2.d4 d5 3.e5

Wikipedia has related information at Caro-Kann.