Spontaneous order, also named self-organization in the hard sciences, is the spontaneous emergence of order out of seeming chaos. The term "self-organization" is more often used for physical changes and biological processes, while "spontaneous order" is typically used to describe the emergence of various kinds of social orders in human social networks from the behavior of a combination of self-interested individuals who are not intentionally trying to create order through planning. Proposed examples of systems which evolved through spontaneous order or self-organization include the evolution of life on Earth, language, crystal structure, the Internet, Wikipedia, and free market economy.

In economics and the social sciences, spontaneous order has been defined by Hayek as "the result of human actions, not of human design".

In economics, spontaneous order has been defined as an equilibrium behavior among self-interested individuals, which is most likely to evolve and survive, obeying the natural selection process "survival of the likeliest".

According to Murray Rothbard, the philosopher Zhuangzi (c. 369–286 BC) was the first to propose the idea of spontaneous order. Zhuangzi rejected the authoritarianism of Confucianism, writing that there "has been such a thing as letting mankind alone; there has never been such a thing as governing mankind [with success]." He articulated an early form of spontaneous order, asserting that "good order results spontaneously when things are let alone", a concept later "developed particularly by Proudhon in the nineteenth [century]".

In 1767, the sociologist and historian Adam Ferguson within the context of Scottish Enlightenment described society as the "result of human action, but not the execution of any human design".

Jacobs has suggested that the term "spontaneous order" was effectively coined by Michael Polanyi in his essay, "The Growth of Thought in Society," Economica 8 (November 1941): 428–56.

The Austrian School of Economics, led by Carl Menger, Ludwig von Mises and Friedrich Hayek made it a centerpiece in its social and economic thought. Hayek's theory of spontaneous order is the product of two related but distinct influences that do not always tend in the same direction. As an economic theorist, his explanations can be given a rational explanation. But as a legal and social theorist, he leans, by contrast, very heavily on a conservative and traditionalist approach which instructs us to submit blindly to a flow of events over which we can have little control.

Many classical-liberal theorists, such as Hayek, have argued that market economies are a spontaneous order, and that they represent "a more efficient allocation of societal resources than any design could achieve." They claim this spontaneous order (referred to as the extended order in Hayek's The Fatal Conceit) is superior to any order a human mind can design due to the specifics of the information required. Centralized statistical data, they suppose, cannot convey this information because the statistics are created by abstracting away from the particulars of the situation.