Geoffrey was probably born some time between 1100 and 1110 in Wales or the Welsh Marches. He must have reached the age of majority by 1129, when he is recorded as witnessing a charter.In his Historia, Geoffrey refers to himself as Galfridus Monumetensis, "Geoffrey of Monmouth", which indicates a significant connection to Monmouth, Wales, and which may refer to his birthplace. Geoffrey's works attest to some acquaintance with the place-names of the region. To contemporaries, Geoffrey was known as Galfridus Artur(us) or variants thereof. The "Arthur" in these versions of his name may indicate the name of his father, or a nickname based on Geoffrey's scholarly interests.Earlier scholars assumed that Geoffrey was Welsh or at least spoke Welsh, However, it is now recognised that there is no real evidence that Geoffrey was of either Welsh or Cambro-Norman descent, unlike for instance, Gerald of Wales. Geoffrey's knowledge of the Welsh language appears to have been slight. He is likely to have sprung from the same French-speaking elite of the Welsh border country as the writers Gerald of Wales and Walter Map, and Robert, Earl of Gloucester, to whom Geoffrey dedicated versions of his Historia Regum Britanniae. It has been argued, by Frank Stenton among others, that Geoffrey's parents may have been among the many Bretons who took part in William I's Conquest and settled in the southeast of Wales. Monmouth had been in the hands of Breton lords since 1075 or 1086 and the names Galfridus and Arthur (if interpreted as a patronymic) were more common among the Bretons than the Welsh. The Bretons and the Welsh spoke a very similar language and even to this day have little difficulty understanding each other.

He may have served for a while in a Benedictine priory in Monmouth. However, most of his adult life appears to have been spent outside Wales. Between 1129 and 1151 his name appears on six charters in the Oxford area, sometimes styled magister ("teacher"). He was probably a secular canon of St. George's college. Oxford castle, All the charters signed by Geoffrey are also signed by Walter, Archdeacon of Oxford, also a canon at that church. Another frequent co-signatory is Ralph of Monmouth, a canon of Lincoln.

On 21 February 1152 Archbishop Theobald consecrated Geoffrey as bishop of St Asaph, having ordained him a priest 10 days before. "There is no evidence that he ever visited his see," writes Lewis Thorpe, "and indeed the wars of Owain Gwynedd make this most unlikely." He appears to have died between 25 December 1154 and 24 December 1155, in 1155 according to Welsh chronicles, when his apparent successor, Richard, took office.

Geoffrey wrote several works of interest, all in Latin, the language of learning and literature in Europe during the medieval period. The earliest one to appear was probably the Prophetiae Merlini (Prophecies of Merlin), which he wrote at some point before 1135, and which appears both independently and incorporated into the Historia Regum Britanniae. It consists of a series of obscure prophetic utterances attributed to Merlin, which Geoffrey claimed to have translated from an unspecified language. In this work Geoffrey drew from the established Welsh tradition of prophetic writing attributed to the sage Myrddin, though his knowledge of Myrddin's story at this stage in his career appears to have been slight. Many of its prophecies referring to historical and political events up to Geoffrey's lifetime can be identified — for example, the sinking of the White Ship in 1120, when William Adelin, son of Henry I, died.

Geoffrey introduced the spelling "Merlin", derived from the Welsh "Myrddin". The Welsh scholar Rachel Bromwich observed that this "change from medial dd > l is curious. It was explained by Gaston Paris as caused by the undesirable associations of the French word merde". The first work about this legendary prophet in a language other than Welsh, it was widely read ... and believed ... much as the prophecies of Nostradamus were centuries later; John Jay Parry and Robert Caldwell note that the Prophetiae Merlini "were taken most seriously, even by the learned and worldly wise, in many nations", and list examples of this credulity as late as 1445.

His major work was the Historia Regum Britanniae (History of the Kings of Britain), the work best known to modern readers. It relates the purported mythical history of Britain, from its first settlement by Brutus, a descendant of the Trojan hero Aeneas, to the death of Cadwallader in the 7th century, taking in Julius Caesar's invasions of Britain, two kings, Leir and Cymbeline, later immortalized by William Shakespeare, and one of the earliest developed narratives of King Arthur.

Geoffrey claims in his dedication that the book is a translation of an "ancient book in the British language that told in orderly fashion the deeds of all the kings of Britain", given to him by Walter, Archdeacon of Oxford. Modern historians have dismissed this claim. It is, however, likely that the Archdeacon furnished Geoffrey with some materials in the Welsh language that helped inspire his work, as Geoffrey's position and acquaintance with the Archdeacon would not have afforded him the luxury of fabricating such a claim outright. Much of it is based on the Historia Britonum, a 9th century Welsh-Latin historical compilation, Bede's Historia ecclesiastica gentis Anglorum and Gildas's sixth-century polemic De Excidio et Conquestu Britanniae expanded with material from Bardic oral tradition, genealogical tracts, and embellished by Geoffrey's own imagination.

Historia Regum Britanniae is now acknowledged as a literary work of national myth containing little reliable history. This has since led many modern scholars to agree with William of Newburgh, who wrote around 1190 that "it is quite clear that everything this man wrote about Arthur and his successors, or indeed about his predecessors from Vortigern onwards, was made up, partly by himself and partly by others". Other contemporaries were similarly unconvinced by Geoffrey's "History". For example, Giraldus Cambrensis recounts the experience of a man possessed by demons: "If the evil spirits oppressed him too much, the Gospel of St John was placed on his bosom, when, like birds, they immediately vanished; but when the book was removed, and the History of the Britons by 'Geoffrey Arthur' (as Geoffrey named himself) was substituted in its place, they instantly reappeared in greater numbers, and remained a longer time than usual on his body and on the book."

However, his major work was widely disseminated across the whole of Medieval Western Europe (Acton Griscom listed 186 extant manuscripts in 1929, and others have been identified since) and it enjoyed a significant afterlife in a variety of forms, including translations/adaptations such as the Anglo-Norman Roman de Brut of Wace, the Middle English Brut of Layamon, and several anonymous Middle Welsh versions known as Brut y Brenhinedd ("Brut of the kings"). where it was generally accepted as a true account.

Furthermore, his structuring and reshaping of the Merlin and Arthur myths engendered the vast popularity of Merlin and Arthur myths in later literature, a popularity that lasts to this day; he is generally viewed by scholars as the major establisher of the Arthurian canon. The Historia's effect on the legend of King Arthur was so vast that Arthurian works have been categorized as "pre-" or "post-Galfridian" depending on whether or not they were influenced by him.

The third work attributed to Geoffrey is another hexameter poem Vita Merlini ("Life of Merlin"). The Vita is based much more closely on traditional material about Merlin than are the other works; here he is known as Merlin of the Woods (Merlinus Sylvestris) or Scottish Merlin (Merlinus Caledonius), and is portrayed an old man living as a crazed and grief-stricken outcast in the forest. The story is set long after the timeframe of Historia's Merlin, but the author tries to synchronize the works with references to the mad prophet's previous dealings with Vortigern and Arthur. The Vita did not circulate widely, and the attribution to Geoffrey appears in only one late 13th century manuscript, but contains recognisably Galfridian elements in its construction and content, and most critics are content to recognise it as his.

Geoffrey of Monmouth was also heavily influenced by old Welsh tales. This can be seen in his works of Arthur from "The History of the Kings of Britain." In which Arthur is seen as having a mysterious conception, as well as having prophecies bestowed upon him. These are two very indicative motifs to old Welsh and older Celtic myths.. This paints a very different picture of Arthur than is seen in Sir Thomas Malory's Le Morte d'Arthur, which is the most famous and well known version of the King Arthur story.

• Geoffrey of Monmouth. "The History of the Kings of Britain." Edited and translated by Michael Faletra. Broadview Books: Peterborough, Ontario, 2008. ISBN 1-55111639-1
• Geoffrey of Monmouth. The History of the Kings of Britain. Translated, with introduction and index, by Lewis Thorpe. Penguin Books: London, 1966. ISBN 0-14-044170-0
• John Jay Parry and Robert Caldwell. "Geoffrey of Monmouth" in Arthurian Literature in the Middle Ages, Roger S. Loomis (ed.). Clarendon Press: Oxford University. 1959. ISBN 0-19-811588-1
• N. J. Higham. King Arthur: Myth-making and History, London and New York, Routledge, 2002, ISBN 0415213053
• John Morris. The Age of Arthur: A History of the British Isles from 350 to 650. Barnes & Noble Books: New York. 1996 (originally 1973). ISBN 1-84212-477-3
• Brynley F. Roberts. "Geoffrey of Monmouth, Historia Regnum Britanniae and Brut y Brenhinedd" in The Arthur of the Welsh: The Arthurian Legend in Medieval Welsh Literature, Cardiff, University of Wales Press, 1991, ISBN 0708313078
• Michael Skupin, including translations of the Vita Merlini.
• Curley, Michael. Geoffrey of Monmouth. New York: Twayne Publishers, 1994.
• Ziolkowski, Jan (1990). "The Nature of Prophecy in Geoffrey of Monmouth's Vita Merlini". In Kugel, James L. (Ed.), Poetry and Prophecy: the Beginnings of a Literary Tradition. Cornell.

English translations available on the web

• Historia Regum Britanniae:
• Histories of the Kings of Britain, tr. by Sebastian Evans, at Sacred Texts
• By Aaron Thompson with revisions by J. A. Giles at http://www.yorku.ca/inpar/geoffrey_thompson.pdf. (PDF)
• (Arthurian passages only) edited and translated by J. A. Giles at http://www.lib.rochester.edu/camelot/geofhkb.htm.
• Vita Merlini, Basil Clarke's English translation from Life of Merlin: Vita Merlini (Cardiff: University of Wales Press, 1973).
• At Jones the Celtic Encyclopedia
• At Sacred-texts.com

???????? ????????Jafrez Menoe??????? ?????????Geoffrey de MonmouthGeoffrey z MonmouthuSieffre o FynwyGeoffrey von Monmouth??????? ??? ????????Godofredo de MonmouthGeoffrey de MonmouthGeoffroy de MonmouthGeoffrey fan MonmouthGodofredo de Monmouth???? ???Goffredo di Monmouth?'??? ???????'Jeffri a VenowGalfridus MonemutensisGeoffrey of MonmouthGeoffrey van Monmouth?????????????Geoffrey av MonmouthGeoffrey av MonmouthGodifré ëd MonmouthGeoffrey of MonmouthGodofredo de MonmouthGeoffrey of Monmouth???????? ??????????Geoffrey od MonmouthaGeoffrey MonmouthilainenGeoffrey av Monmouth???????????????????????? ???????????