The Colle System, also known as the Colle–Koltanowski system, is a chess opening strategy for White introduced by Belgian Edgard Colle in the 1920s, and further developed by George Koltanowski. This variation of the Queen's Pawn Game is characterised by a systematic if modest development of White's minor pieces to support a quick pawn move to the e4 square. It is solid, but inflexible.
Colle and Koltanowski each won many tournaments in the '20s and '30s. 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, a decent endgame, and it gives White “good chances of not losing against a stronger player”. However, players, like Capablanca and Tal have found ways to take the sting out of some of its various lines.
Ignoring Black's responses in order to consider White's moves only, the typical plan is as follows: 1.d4 d5 2.Nf3 Nf6 3.e3 e6 4.Bd3 with White rearranging his move order appropriately. It is a perfectly solid scheme of development, but, inflexibly applied, it cannot offer more than equality against a vigorous Black response. It may be a good tool for avoiding book variations, for Blitz play, or for forcing opponents to think for themselves early on. These days it is considered totally innocuous, and is rarely seen at Master level or above.
One variation on the Colle is the Colle–Zukertort System (named for Johannes Zukertort), characterized 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. In this variation White will eventually play for a kingside Attack, despite his apparently innocuous development. This system has been frequently employed at grandmaster level by Artur Yusupov.
Queen's Pawn Game, Zukertort Variation (including Colle system)