The green children of Woolpit reportedly appeared in the village of Woolpit in Suffolk, England, some time in the 12th century, perhaps during the reign of King Stephen. The children, brother and sister, were of generally normal appearance except for the green colour of their skin. They spoke in an unknown language, and the only food they would eat was green beans. Eventually they learned to eat other food and lost their green pallor, but the boy was sickly and died soon after the children were baptised. The girl adjusted to her new life, but she was considered to be "rather loose and wanton in her conduct". After she learned to speak English the girl explained that she and her brother had come from St Martin's Land, an underground world whose inhabitants are green.

The only near-contemporary accounts are contained in Ralph of Coggeshall's Chronicum Anglicanum and William of Newburgh's Historia rerum Anglicarum, written in about 1189 and 1220 respectively. Between then and their rediscovery in the mid-19th century, the green children seem to surface only in Bishop Francis Godwin's fantastical The Man in the Moone, in which William of Newburgh's account is reported.

Two approaches have dominated explanations of the story of the green children: that it is a typical folk tale describing an imaginary encounter with the inhabitants of another world, perhaps one beneath our feet or even extraterrestrial, or it is a garbled account of a historical event. The story was praised as an ideal fantasy by the English anarchist poet and critic Herbert Read in his English Prose Style, published in 1931. It provided the inspiration for his only novel, The Green Child, written in 1934.

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