A singleton is a world order in which there is a single decision-making agency at the highest level. The singleton hypothesis is the hypothesis that Earth-originating intelligent life will eventually assume the form a singleton.

The concept of a singleton expresses an abstract idea. A singleton could take the form of world government, such as global democracy or global totalitarianism, but this need not be so. What is required for humanity to constitute a singleton is for it to behave roughly like a coherent agent.^[1][2]