World government is the concept of a single political authority with jurisdiction over all humanity. It is conceived in a variety of forms, from tyrannical to democratic, which reflects its wide array of proponents and detractors.

A world government with executive, legislative, and judicial functions and an administrative apparatus has never existed. The inception of the United Nations (UN) in the mid-20th century remains the closest approximation to a world government, as it is by far the largest and most powerful international institution. However, the UN is mostly limited to an advisory role, with the stated purpose of fostering cooperation between existing national governments, rather than exerting authority over them. Nevertheless, the organization is commonly viewed as either a model for, or preliminary step towards, a global government.

The concept of universal governance has existed since antiquity and been the subject of discussion, debate, and even advocacy by some kings, philosophers, religious leaders, and secular humanists. Some of these have discussed it as a natural and inevitable outcome of human social evolution, and interest in it has coincided with the trends of globalization. Opponents of world government, who come from a broad political spectrum, view the concept as a tool for violent totalitarianism, unfeasible, or simply unnecessary, and in the case of some sectors of fundamentalist Christianity, as a vehicle for the Antichrist to bring about the end-times.

World government for Earth is frequently featured in fiction, particularly within the science fiction genre; well-known examples include the "World State" in Aldous Huxley's Brave New World, the "Dictatorship of the Air" in H. G. Wells' The Shape of Things to Come, the United Nations in James S. A Corey's The Expanse, and United Earth (amongst other planetary sovereignties and even larger polities) in the Star Trek franchise. This concept also applies to other genres, while not as commonly, including well known examples such as One Piece.