In an alternate 2015, Earth faces an unprecedented extraterrestrial assault that compels the world's nations to establish XCOM, a unified military-scientific coalition devoted to planetary defense. As the organization's commander, the player must lead tactical operations against technologically superior invaders while simultaneously researching alien biology and weaponry to reverse-engineer their technology for humanity's advantage. Caught between immediate battlefield survival and the long-term intelligence race, XCOM stands as humanity's last hope against an enemy whose true motives remain shrouded in mystery.