Yes, you can play both the campaign mode and multiplayer mode in Call of Duty: Modern Warfare 3 offline. The campaign mode can be played in its entirety in offline mode, and a Private Multiplayer mode allows you to access all of the maps and modes present in Multiplayer.

Call of Duty 4: Modern Warfare is a first person shooter game for the PC, Playstation 3, Xbox 360, and Nintendo DS. All four platforms have multiplayer capability but only the PC, PS3 and Xbox 360 have the ability to play the game online.