London System

The London System arises after 1. d4 d5 2. Nf3 Nf6 3. Bf4. White develops the dark-squared bishop outside the pawn chain first, so that the later e3, which reinforces d4, does not shut it in. This is the main difference from the Colle System with 3. e3, where that bishop stays behind the pawns. The same position often comes from the Accelerated London, 1. d4 d5 2. Bf4 Nf6 3. Nf3.

The London is a true system. White aims for the same arrangement against most Black setups: pawns on d4 and e3, the bishop on f4, and a knight that can settle on e5, where the d4-pawn and the f4-bishop support it. The move order inside that scheme is flexible, so the opening needs far less memorization than the Queen's Gambit lines. The setup has a known cost. Once the bishop leaves c1, b2 has less protection, and Black's most pointed plans combine ...c5 against d4 with ...Qb6 against the b-pawn.

The most common reply is 3...e6. It leads to the London System with e6, a position also reached by 1. d4 d5 2. Nf3 e6 3. Bf4. Black builds a compact center and accepts that the c8-bishop sits behind the e6-pawn. The next most frequent replies are 3...Nc6 and 3...Bf5. White scores rather better against the knight move. The bishop move mirrors White's idea by getting Black's queen's bishop out before ...e6. Engines also rate 3...c5 among the best options, since it hits d4 at once and prepares the queenside pressure.

The Pterodactyl Variation is also filed under the London name, although it arises from a different setup: 1. d4 g6 2. Nf3 Bg7 3. Bf4 c5 4. c3 cxd4 5. cxd4 Qa5+. Black fianchettoes, opens the c-file and develops the queen with check instead of contesting the center with ...d5.

The main line is among the more frequently reached named positions, with close to 185,000 Lichess games. The engine rates it as balanced, while White scores somewhat better than Black in practice. Play tends to be maneuvering and low on forcing theory.