The Territorial Imperative: A Personal Inquiry Into the Animal Origins of Property and Nations is a 1966 nonfiction book by American writer Robert Ardrey. It characterizes an instinct among humans toward territoriality and the implications of this to property ownership and nation building. The Territorial Imperative was influential at the time, and encouraged public interest in human origins.

The Territorial Imperative is the second book in Ardrey's Nature of Man Series; it is preceded by African Genesis (1961) and followed by The Social Contract (1970) and The Hunting Hypothesis (1976). It was illustrated by Ardrey's wife, the South African actress and illustrator Berdine Ardrey (née Grunewald). Ardrey dedicated The Territorial Imperative to Henry Eliot Howard, who was noted for being one of the first to describe in detail the territorial behaviors of birds.

The Territorial Imperative develops the theses originally introduced in African Genesis: A Personal Investigation into the Animal Origins and Nature of Man, which was published five years earlier. In African Genesis, Ardrey posited that man originated in Africa instead of Asia, that he is driven by inherited instincts to acquire land and defend territory, and that the development of weapons was a fundamental turning point in his evolution. The Territorial Imperative further explores these ideas with a special emphasis on man's distinct preoccupation with the concept of territory. It goes on to elucidate the role that plays in modern human society in phenomena such as property ownership and nation building.

The Territorial Imperative caused significant scientific and popular controversy. In it Ardrey restated and developed his challenge to the reigning methodological assumption of the social sciences, that human behavior is fundamentally distinct from animal behavior. As he writes in The Territorial Imperative, "The dog barking at you from behind his master's fence acts for a motive indistinguishable from that of his master when the fence was built." Robert Wokler wrote of Ardrey's challenge to the established life sciences:

What ought to be studied, according to Ardrey, are the relations between individuals that stem from the innate and universal attributes of animal life, whereas cultural anthropologists who detect a fundamental discontinuity between mankind and other zoological species are just impervious to the revolutionary ideas of Darwinism which have reverberated throughout all the life sciences apart from their own.

In 1968, two years after the publication of The Territorial Imperative, Ashley Montagu organized fourteen scientists to write essays in opposition to Ardrey's work (and the similarly aligned work of Konrad Lorenz, On Aggression). That volume became Man and Aggression. Montagu would eventually edit another volume in opposition to Ardrey, and the increasingly heated debate stirred popular interest in human origins. By Carmel Schrire's account, "Ashley Montagu edited two collections of writings aimed at countering the views of both Ardrey and Konrad Lorenz. ... Despite this, Ardrey's popularity did not flag, and his writings opened the fields of paleoanthropology, ethnology, and anthropology to a wide readership."

The opposition of these two viewpoints became a major theme in the social science of the time. Robin Fox, who authored The Imperial Animal (1972) with Lionel Tiger, wrote of the opposition:

I was a great friend of Robert Ardrey, and had been known publicly to defend his name and honor from the assault of the anti-Ardreyites, including Ashley Montagu. ... Ashley Montagu always carefully distanced himself from what he thought were our erroneous conclusions about human aggression. We returned the favor, even calling him and his school "the Christian Scientists of anthropology" for their refusal to accept the reality of human evil: that it was an essential part of being human and could not be just wished away. We in turn were included eventually among the villains in his "new litany of innate depravity." And so it went.