X is the name of the game. It is a simple card game that models diplomatic relations between countries with regard to nuclear weapons and disarmament.
In the game, colored cards with shapes on them represent non-nuclear sources of power and influence on the international stage. X cards represent nuclear weapons. Players match and trade shape cards according to certain rules. This process models negotiation, cultural influence, and trade. Players also discard X cards through a defined process that makes them less powerful in the short term but helps them to win the game. The game ends when any player has discarded all of their X cards.
The goal of the game is to amass the shape cards through normal gameplay, while simultaneously discarding X cards. However, X cards give players leverage over other players with fewer X cards, so it is important for players to discard strategically and in cooperation.
Just as with nuclear weapons, any player possessing an X card puts all players at risk, and the more undiscarded X cards there are in play, the greater the risk for everyone. Additionally, players are penalized for continuing to hold X cards when the game ends.