If you picked up the recent Red Orchestra 2: Heroes of Stalingrad on Steam or at retail, you may be having trouble finding the game's co-op mode. We'll save yourself some time, and have you stop your search right now, because the game is currently missing the planned co-op mode. There's an update to the game that'll be available in the coming weeks, after the developers wrap up the "post release fix those bloody bugs" phase, which will add the campaign co-op play in.
Currently there's no set time frame for the update, but keep checking back with us as we'll update you as soon as we have more info.