London System

The London System is a chess opening that usually arises after 1.d4 and 2.Bf4, or 1.d4, 2.Nf3 and 3.Bf4. It is a "" opening that can be used against virtually any black defense and thus comprises a smaller body of opening theory than many other openings. The London System is one of the Queen's Pawn Game openings where White opens with 1.d4 but does not play the Queen's Gambit. It normally results in a . The line can be compared to the Colle System but whereas in the latter system, the queen's bishop remains on c1, the London System develops the bishop to f4 before closing the position, providing a more flexible approach. 
Sverre Johnsen and Vlatko Kovačević, in the introduction to their 2005 book "Win with the London System", state: 
Essentially, the London is a set of solid lines where after 1.d4 White quickly develops their dark-squared bishop to f4 and normally bolsters their centre with [pawns on] c3 and e3 rather than expanding. Although it has the potential for a quick kingside attack, the white forces are generally flexible enough to engage in a battle anywhere on the board. Historically it developed into a system mainly from three variations: 
The corresponding "Encyclopaedia of Chess Openings" codes are D02, A46, and A48. 
Description.
The line came into fashion in the 1922 London tournament as a way of meeting hypermodern setups. The line gives White a position, and critics of the line refer to it as the "old man’s variation" or the "boring system". Even so, the opening can lead to attacks. Vlatko Kovačević and David Bronstein are among the sharp tactical players who have played the London System.
Early play.
1.d4 d5 2.Nc3 Nf6 3.Bf4.
This line is often known as the Jobava London system, named after Baadur Jobava.
1.d4 d5 2.Nf3 Nf6 3.Bf4.
This position can also be reached via 1.d4 Nf6 2.Nf3 d5 3.Bf4. Black usually plays either 3...c5, 3...e6, 3...Bf5, 3...c6, 3...g6, or 3...Nc6.
1.d4 Nf6 2.Nf3 e6 3.Bf4.
Black usually plays either 3...b6, 3...c5, or 3...d5, transposing above.
1.d4 Nf6 2.Nf3 g6 3.Bf4.
Play often goes 3...Bg7 4.e3 d6 5.Be2 0-0 6.0-0. As is usual in the King's Indian, Black can strike in the centre with ...c5 or ...e5. After 6...c5 7.c3, Black often plays either 7...b6, 7...Qb6, 7...Nc6, 7...Be6, or 7...cxd4. Black can prepare ...e5 in a number of ways, usually starting with either 6...Nbd7, 6...Nc6, or 6...Nfd7.
Afterwards, if unimpeded by Black's moves, White ideally would like to build a pyramid of pawns centered on d4 and develop all minor pieces. This could be achieved in various orders, for example, 1.d4, 2.Bf4, 3.Nf3, 4.e3, 5.c3, 6.Nbd2, 7.Bd3.