Nimzo-Indian defence

The Nimzo-Indian defence is a popular chess opening with these initial moves: 1.d4 Nf6 2.c4 e6 3.Nc3 Bb4. The basic idea is for Black to challenge for control of the central square e4. This comes at the cost of exchanging his Bb4 for the white Nc3 when White plays a3. The opening is named after Aaron Nimzovich, who developed and promoted it. Initially a hypermodern opening, it usually transposes (changes) into classical form, as black occupies central squares by ...c5 and ...d5.
The white central pawns are under restraint. Much preparation is needed before they can move forward.