The Green Man, also known as a foliate head, is a motif in architecture and art, of a face made of, or completely surrounded by, foliage, which normally spreads out from the centre of the face. Apart from a purely decorative function, the Green Man is primarily interpreted as a symbol of rebirth, representing the cycle of new growth that occurs every spring.

The Green Man motif has many variations. Branches or vines may sprout from the mouth, nostrils, or other parts of the face, and these shoots may bear flowers or fruit. Found in many cultures from many ages around the world, the Green Man is often related to natural vegetation deities. Often used as decorative architectural ornaments, where they are a form of mascaron or ornamental head, Green Men are frequently found in architectural sculpture on both secular and ecclesiastical buildings in the Western tradition. In churches in England, the image was used to illustrate a popular sermon describing the mystical origins of the cross of Jesus.

"Green Man" type foliate heads first appeared in England during the early 12th century deriving from those of France, and were especially popular in the Gothic architecture of the 13th to 15th centuries. The idea that the Green Man motif represents a pagan mythological figure, as proposed by Lady Raglan in 1939, despite its popularity with the lay public, is not supported by evidence.

Usually referred to in art history as foliate heads or foliate masks, representations of the Green Man take many forms, but most just show a "mask" or frontal depiction of a face, which in architecture is usually in relief. The simplest depict a man's face peering out of dense foliage. Some may have leaves for hair, perhaps with a leafy beard. Often leaves or leafy shoots are shown growing from his open mouth and sometimes even from the nose and eyes as well. In the most abstract examples, the carving at first glance appears to be merely stylised foliage, with the facial element only becoming apparent on closer examination. The face is almost always male; green women are rare. Lady Raglan coined the term "Green Man" for this type of architectural feature in her 1939 article The Green Man in Church Architecture in The Folklore Journal. It is thought that her interest stemmed from carvings at St. Jerome's Church in Llangwm, Monmouthshire.

The Green Man appears in many forms, with the three most common types categorized as:

In terms of formalism, art historians see a connection with the masks in Iron Age Celtic art, where faces emerge from stylized vegetal ornament in the "Plastic style" metalwork of La Tène art. Since there are so few survivals, and almost none in wood, the lack of a continuous series of examples is not a fatal objection to such a continuity.

The Oxford Dictionary of English Folklore suggests that they ultimately have their origins in late Roman art from leaf masks used to represent gods and mythological figures. A character superficially similar to the Green Man, in the form of a partly foliate mask surrounded by Bacchic figures, appears at the centre of the 4th-century silver salver in the Mildenhall Treasure, found at a Roman villa site in Suffolk, England; the mask is generally agreed to represent Neptune or Oceanus and the foliation is of seaweed.

In his lectures at Gresham College, historian and professor Ronald Hutton traces the green man to India, stating "the component parts of Lady Raglan's construct of the Green Man were dismantled. The medieval foliate heads were studied by Kathleen Basford in 1978 and Mercia MacDermott in 2003. They were revealed to have been a motif originally developed in India, which travelled through the medieval Arab empire to Christian Europe. There it became a decoration for monks’ manuscripts, from which it spread to churches."