Spontaneous order explains how complex and useful social institutions arise without anyone designing them, and how such institutions can embody more practical knowledge than any designer could assemble. Markets, language, money, common law and custom are the standard examples.
Its classic formulation is Adam Ferguson's: nations stumble upon establishments which are indeed the result of human action but not the execution of any human design. Menger gave the idea an economic demonstration by explaining how money could emerge from barter through individually rational choices with no collective decision anywhere. Hayek made it the center of his mature political thought. His distinction between cosmos, a grown order, and taxis, a made one, underwrites the argument that the rules of a free society are found and refined instead of legislated, and that the fatal conceit of planning is not that planners lack good intentions but that the knowledge they would need does not exist in a form anyone can collect.
The concept is among the most influential in contemporary political and economic thought, and it supplies the strongest general argument against large-scale social engineering. It travels well beyond economics. Evolutionary biology, the growth of scientific knowledge and the development of language are all standardly described in these terms.
Its recurring misuse is the inference from emergent to good. Spontaneous orders include cartels, castes, feuds, segregated housing patterns and entrenched corruption. All arise without design and none is thereby justified. Hayek denied making the inference, but critics argue his framework supplies no criterion for telling the orders worth preserving from those worth dismantling, which is exactly the question politics has to answer.