A Gaian is a radical Green who views the ecology of the Earth's biosphere not only as the basis of human moral examples, but of all cognition and even sentience. Advocates of this view claim that since we live as part of one planet's photosynthesis chain and trapped within its gravity well, we are effectively components of one large body—that being the global ecology of Earth itself.

Another name for this value theory is "radical values environmentalism"—individuals and societies are ways to create such a thriving ecosystem, but cannot be considered as being ends in themselves.

An early advocate of this view was Buckminster Fuller who developed the Dymaxion Map of the world, the first world projection to show the continents on a flat surface without visible distortion—and the earth as being essentially one island in one ocean. In Critical Path, 1981, he claimed to prove that "gravity is love". Critics say this view makes humans "slaves of the Earth" and argue that human destiny is to spread out to find or form many living worlds. In contrast, some Gaians see such colonists as locusts or a disease, and may see all human beings as elements of a single Earth-wide ecology, if not organism. They are often hard to differentiate from members of the New Age movement, with which they share the goal of deep spiritual integration.

Political Gaians are a relatively recent offshoot of the ecology movement—and get their name from the Gaia hypothesis, a scientific theory first developed by James Lovelock.

This holds that the biosphere tends to homeorhetic balance or even homeostasis with the implication that human beings should be working toward such balances or states. Or, in more radical terms, as part of an Earth immune system.

Activist Gaians are sometimes described as terrists although this label is controversial—and designed to encourage and evoke such controversy. There is no obvious or certain connection between the Gaian philosophy and the action of terrists—or terrorists. New Age Gaians in particular seem to resent this label, as their goals are spiritual not material.

See also: Gaia theory (science)

In the computer game Sid Meier's Alpha Centauri, the Gaians are one of the seven factions the player can choose to control. Their philosophy in the game is similar to that described in this article.

Gaian is a term used when referring to a user of the popular forum Gaia Online. Or spoken in reference to the Avatar character used to represent oneself in the forum.