The Green Man is primarily considered a symbol of rebirth, representing the cycle of growth each spring, but it can also be related to natural vegetative deities. Some researchers speculate that the mythology of the Green Man developed independently in the traditions of separate ancient cultures and evolved into the wide variety of examples found throughout history.
Usually referred to in works on architecture as foliate heads or foliate masks, carvings of the Green Man may take many forms, naturalistic or decorative. 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, but green cats, lions, and demons are also found. On gravestones and other memorials, human skulls are sometimes shown sprouting grape vines or other vegetation, presumably as a symbol of resurrection. The Green Man appears in many forms, with the three most common types categorized as: the Foliate Head (completely covered in green leaves), the Disgorging Head (spews vegetation from its mouth) and the Bloodsucker Head (sprouts vegetation from all facial orifices).
Superficially the Green Man would appear to be pagan, perhaps a fertility figure or a nature spirit, similar to the woodwose, and yet he frequently appears, carved in wood or stone, in churches, chapels, abbeys and cathedrals. The earliest example of a green man disgorging vegetation from his mouth is from St. Abre, in St. Hilaire-le-grand, c 400 AD. To the modern observer the earlier (Romanesque and medieval) carvings often have an unnervingly eerie or numinous quality. This is sometimes said to indicate the vitality of the Green Man, who was able to survive as a symbol of pre-Christian traditions despite, and at the same time complementary to, the influence of Christianity: rather than alienate their new converts, early Christian missionaries would often adopt and adapt local gods, sometimes turning them into saints.
Parallels have been drawn between the Green Man and various deities such as the British Celtic Lud, also known as Nodens. Many see him as being connected to the Mesopotamian Tammuz who is thought to symbolize the triumph of Life over Winter and Death, Osiris, Odin, and even Jesus, as well as later folkloric and literary characters such as the Holly King.