Bent on Humankind's extermination, a powerful fellowship of alien races known as the Covenant is wiping out the Earth's fledgling interstellar empire. You and the other surviving defenders of a devastated colony-world make a desperate attempt to lure the alien fleet away from Earth. Shot down and marooned on the ancient ring-world Halo, you begin a guerilla-war against the Covenant. Fight for humanity against an alien onslaught as you race to uncover the mysteries of Halo. Halo, the award-winning and critically acclaimed science fiction epic adventure, is coming to the PC, courtesy of Bungie and Gearbox Software. Packed with action, Halo contains all the thrilling gameplay and rich story that made it a smash hit with gamers all over the world. Now you can take the battle online with all new multiplayer including new maps, weapons and vehicles available only on your PC!

Microsoft.com