The Nimzo Indian Defense is an extremely solid defense that is seen at all levels of play. Many players playing as white will try different variations to try to avoid going into the Nimzo Indian Defense lines.
1. d4 Nf6
2. c4 e6
3. Nc3 Bb4
Black looks to double up the pawns on the c-file in exchange for his dark square bishop. With the knight on c3 the key defender of the e4 square, black really starts to focus his energy on controlling the e4 and the light squares.
This defense has many different variations and you could spend the rest of your life just trying to cover half of them. The good thing is that there are many ways to mix up your play and keep your opponents guessing. If you are a strategic player that likes to methodically build up a strong game plan and dominate your opponent in the middle/end game then I highly recommend you try this opening.
Watch the video below to watch more detailed explanations of the opening, multiple variations, and extended lines.