Colle System

The Colle System, also known as the Colle–Koltanowski System, is a chess opening for White, popularised in the 1920s by the Belgian master Edgard Colle and further developed by George Koltanowski.

The Colle is characterised by several moves. White's center pawns are to d4 and e3, the king's knight is developed to f3, the king's bishop is developed to d3, and the queen bishop's pawn (c-pawn) is developed to c3. Common continuations include development of the queen's knight to d2 (Nbd2) and castling (0-0). A major theme of the Colle System is the ambition to play a well-timed e4, where the square is defended by the bishop on d3, the knight on d2 (following Nbd2), and possibly the rook on e1 (following 0-0 and Re1). Although sometimes described as a specific sequence of moves, the Colle System is not a fixed line of play, but rather a system for White where the moves may be permuted at the player's discretion. When a game opens with most or all of the above moves, to the exclusion of moves which typify other openings, the game may be described as "a Colle System".

Although criticised by some and used infrequently in master play, the Colle is regarded by others as a and  opening.

Definition and assessment
The Encyclopaedia of Chess Openings (ECO) identifies the Colle System as an uncommon continuation of the Queen's Pawn Game, assigning it the code D05. In the ECO, the Colle system is defined by the line 1.d4 d5 2.Nf3 Nf6 3.e3 e6 4.Bd3 c5 5.c3. Paul van der Sterren gives an identical definition, with the same moves played in the same order. Other authors clarify that the system refers specifically to White's moves. Hooper and Whyld define the Colle as d4, Nf3, e3, Nbd2, c3 and Bd3 (in no particular order), including Nbd2 in their definition rather than noting it as a usual continuation. Benjamin and Schiller give the broader, less specific definition 1.d4, 2.Nf3, 3.e3, although they also note that the immediate plan involves developing the "f1-bishop".

John Nunn et al. regard the Colle as totally innocuous. While acknowledging the system's "innocuous" reputation and its "slow and solid" plan of development, Benjamin and Schiller recommended the Colle as a "good" example of an unorthodox opening, as opposed to a "bad" or "ugly" one. Together with Benjamin and Schiller, Hooper and Whyld also noted that the Colle is unfashionable in master play. Van der Sterren concurred with Benjamin and Schiller that the Colle is a fine opening "for those who want to keep the opening as simple as possible", and also echoed their remark that White's plan is to play e4 in the near future.

History
Colle and Koltanowski each won several tournaments in the 1920s and 1930s. Colle finished ahead of Tartakower, Euwe, and Rubinstein at various times. The opening had even been referred to as the "dreaded" Colle System. George Koltanowski, in his book The Colle System, said it offered "solid development", combinations, and a decent endgame, giving White "good chances of not losing against a stronger player". Players like Capablanca and Tal found ways to take the sting out of some of its various lines, however. One such line that has been tested is 3...Bf5, sometimes called the "Anti-Colle". Magnus Carlsen lost his only game with the white pieces during his five world championship matches, when he played the Colle-Zukertort System in game 8 of the World Chess Championship 2016 against Sergey Karjakin. The Colle was seen once again in world championship play in 2023, when Ding Liren successfully employed the system against Ian Nepomniachtchi in winning game 12 of the World Chess Championship 2023. Ding's compatriot Wei Yi also successfully employed the use of the Colle System in round 13 of the Tata Steel Chess Tournament 2024, defeating Vidit Gujrathi on route to the playoffs, with Wei Yi eventually winning the Masters section of the tournament.

Colle–Zukertort System
One variation of the Colle is the Colle–Zukertort System (named after Johannes Zukertort), characterised by developing the dark-squared bishop on b2. The typical plan is: 1.d4 d5 2.Nf3 e6 3.e3 Nf6 4.Bd3 c5 5.b3 Nc6 6.0-0 Bd6 7.Bb2 0-0, where White, despite their apparently innocuous development, will eventually play for a kingside attack. This system has been frequently employed at grandmaster level by Artur Yusupov.

Games
A famous Colle System win featuring a slightly unusual Greek gift sacrifice is Colle–O'Hanlon, 1930. Analysts have debated the theoretical soundness of this sacrifice for many years.

Black has a variety of approaches to counter the Colle System. One of the most dynamic is to aim for a Queen's Indian Defense setup. White's pawn to e4 slashes at empty space, while Black's pieces are poised to undermine White's  and attack the. The technique is well-illustrated in the 1929 game between Colle and José Capablanca: