Queen's Gambit Declined

3...Nf6

Here white can take an interesting departure from the typical QGD lines by playing 4. g3, transposing into a main line of the Catalan Opening. This colorful opening can be very aggressive, especially if black opens the long diagonal with ...dxc4 at some point. The piece play white obtains from such an opening of lines is often dangerous for black.

At this point, white's other main continuations are 4. Nc3 and 4. Bg5, though 4. cxd5 is certainly possible.