Christianity was probably introduced to what is now Lowland Scotland by Roman soldiers stationed in the north of the province of Britannia. After the collapse of Roman authority in the fifth century, Christianity is presumed to have survived among the British enclaves in the south of what is now Scotland, but retreated as the pagan Anglo-Saxons advanced. Scotland was largely converted by Irish missions associated with figures such as St Columba, from the fifth to the seventh centuries. These missions founded monastic institutions and collegiate churches that served large areas. Scholars have identified a distinctive form of Celtic Christianity, in which abbots were more significant than bishops, attitudes to clerical celibacy were more relaxed and there were significant differences in practice with Roman Christianity, particularly the form of tonsure and the method of calculating Easter, although most of these issues had been resolved by the mid-seventh century. After the reconversion of Scandinavian Scotland in the tenth century, Christianity under papal authority was the dominant religion of the kingdom.

In the Norman period, from the eleventh to the thirteenth centuries, the Scottish church underwent a series of reforms and transformations. With royal and lay patronage, a clearer parochial structure based around local churches was developed. Large numbers of new monastic foundations, which followed continental forms of reformed monasticism, began to predominate. The Scottish church also established its independence from England, developing a clear diocesan structure and becoming a "special daughter of the see of Rome", but continued to lack Scottish leadership in the form of archbishops.

In the late Middle Ages the problems of schism in the Catholic Church allowed the Scottish Crown to gain greater influence over senior appointments and two archbishoprics had been established by the end of the fifteenth century. Historians have discerned a decline in traditional monastic life in the late Middle Ages, but the mendicant orders of friars grew, particularly in the expanding burghs, emphasised preaching and ministering to the population. New saints and cults of devotion also proliferated. Despite problems over the number and quality of clergy after the Black Death in the fourteenth century, and evidence of heresy in the fifteenth century, the church in Scotland remained stable before the Reformation in the sixteenth century.

Early Middle Ages

Early Christianisation

Before the Middle Ages, most of the population of what is now Scotland practised a form of Celtic polytheism.B. Cunliffe, The Ancient Celts (Oxford: Oxford University Press, 1997), , p. 184.P. Dunbavin, Picts and Ancient Britons: an Exploration of Pictish Origins (Third Millennium Publishing, 1998), , p. 41. Evidence of Christian symbols and the destruction of the shrines of other religions, suggest that Roman occupation brought Christianity to the north of Britannia (the name they gave to the province under their control in the southern part of the island). From there it may have spread to parts of what they called Caledonia (roughly corresponding to what is now Scotland).L. Alcock, Kings and Warriors, Craftsmen and Priests in Northern Britain AD 550–850 (Edinburgh: Society of Antiquaries of Scotland), , p. 63.Lucas Quensel von Kalben, "The British Church and the Emergence of the Anglo-Saxon Kingdom", in T. Dickinson and D. Griffiths, eds, Anglo-Saxon Studies in Archaeology and History, 10: Papers for the 47th Sachsensymposium, York, September 1996 (Oxford: Oxford University Press, 1999), , p. 93. After the collapse of Roman authority in the early fifth century, four major circles of influence emerged in Northern Britain. In the east were the Picts, whose kingdoms eventually stretched from the river Forth to Shetland. In the west were the Gaelic (Goidelic)-speaking people of Dál Riata, who had close links with Ireland, from where they brought with them the name Scots. In the south were the British (Brythonic-speaking) descendants of the peoples of the Roman-influenced kingdoms of "The Old North", the most powerful and longest surviving of which was the Kingdom of Strathclyde. Finally, there were the English or "Angles", Germanic invaders who had overrun much of southern Britain and held the Kingdom of Bernicia (later the northern part of Northumbria), which reached into what are now the Borders of Scotland in the south-east.J. R. Maddicott and D. M. Palliser, eds, The Medieval State: essays presented to James Campbell (London: Continuum, 2000), , p. 48. While the Picts and Scots would have remained pagan, most scholars presume that Christianity would have survived after the departure of the Romans among the Brythonic enclaves, but retreated as the pagan Anglo-Saxons advanced.O. Davies, Celtic Spirituality (Mahwah, NJ: Paulist Press, 1999), , p. 21.

The Christianisation of Scotland was carried out by Irish-Scots missionaries and to a lesser extent those from Rome and England. Richard Fletcher argued that motivations may have included the example of St. Patrick, the idea of Peregrinatio and a growing interest in evangelism.R. A. Fletcher, The Barbarian Conversion: From Paganism to Christianity (University of California Press, 1999), , pp. 231–3. In the sixth century missionaries from Ireland were operating on the British mainland. This movement is traditionally associated with the figures of St Ninian, St Kentigern and St Columba. Ninian is now regarded as a later construct and may have been the result of scribal confusion with the Irish saint Finnian.R. A. Fletcher, The Barbarian Conversion: from Paganism to Christianity (Berkeley CA: University of California Press, 1999), , pp. 79–80.Thomas Owen Clancy, "The real St Ninian", The Innes Review, 52 (2001). There was a church dedicated to him at Whithorn in the sixth century and from there St Kentigern seems to have created a new centre of worship at Govan or Inchinnan, from where Christian influence extended across the Strathclyde region.A. Macquarrie, Medieval Scotland: Kinship and Nation (Thrupp: Sutton, 2004), , p. 46.B. Webster, Medieval Scotland: the Making of an Identity (New York City, NY: St. Martin's Press, 1997), , pp. 50–1. St Columba was probably a disciple of Finnian. He left Ireland after being exiled, and founded the monastery at Iona off the west coast of Scotland in 563. From there missions were carried out to western Argyll and the islands around Mull. Later the influence of Iona would extend to the Hebrides. In the seventh century, St. Aidan went from Iona to found a church at Lindisfarne off the east coast of Northumbria. The influence of Lindisfarne would spread through the kingdom of Northumbria into what is now south-east Scotland. The result was a series of overlapping and informally organised churches.B. Webster, Medieval Scotland: the Making of an Identity (New York City, NY: St. Martin's Press, 1997), , p. 51. Iona emerged as the most important religious centre, partly as a result of the work of Adomnan, who was abbot there from 679 to 704. Although it is unclear whether the historic Columba did conduct missions outside of a small part of Dál Riata, Adomnan's Life of St. Columba elevated him to become the apostle of North Britain in general.B. Webster, Medieval Scotland: the Making of an Identity (New York City, NY: St. Martin's Press, 1997), , pp. 52–3.

The means and speed by which the Picts converted to Christianity is uncertain.B. Webster, Medieval Scotland: the Making of an Identity (New York City, NY: St. Martin's Press, 1997), , p. 53. The process may have begun early.O. Clancy, "The Scottish provenance of the 'Nennian' recension of Historia Brittonum and the Lebor Bretnach" in: S. Taylor, ed., Picts, Kings, Saints and Chronicles: A Festschrift for Marjorie O. Anderson (Dublin: Four Courts, 2000), pp. 95–6 and A. P. Smyth, Warlords and Holy Men: Scotland AD 80–1000 (Edinburgh: Edinburgh University Press, 1989), , pp. 82–3. Evidence for this includes the fact that St. Patrick, active in the fifth century, referred in a letter to "apostate Picts", indicating that they had previously been Christian, but had abandoned the faith. In addition the poem Y Gododdin, set in the early sixth century and probably written in what is now Scotland, does not remark on the Picts as pagans.G. Markus, "Conversion to Christianity", in M. Lynch, ed., The Oxford Companion to Scottish History (Oxford: Oxford University Press, 2001), , pp. 78–9. Conversion of the Pictish élite seems likely to have run over a considerable period, beginning in the fifth century and not complete until the seventh and conversion of the general population may have stretched into the eighth century.

Among the key indicators of Christianisation are cemeteries containing long cists which are generally east–west in orientation.E. Proudfoot, "The Hallow Hill and the Origins of Christianity in Eastern Scotland", in B. E. Crawford, ed., Conversion and Christianity in the North Sea World: The Proceedings of a Day Conference held on 21 February 1998, St John's House Papers (St. Andrews, University of St. Andrews Press: 1998), , pp. 57 and 67–71. These cemeteries are suspected, or known to be Christian, because of their proximity to a church, or because of Christian inscriptions found in them.E. Proudfoot, "Archaeology and Early Christianity in Scotland", in E. H. Nicol, ed., A Pictish Panorama (Balgavies, Angus: Pinkfoot Press, 1995), , pp. 27–8. They are found for between the end of the Roman era in the early fifth century and the twelfth century. They are concentrated strongly in eastern Scotland south of the River Tay, in the modern East and Borders of Scotland.S. Foster, Picts, Gaels and Scots: Early Historic Scotland (London, 2004), , p. 77. Most scholars agree that the place-name element eccles-, from the Brythonic word for church, represents evidence of the British church of the Roman and immediate post-Roman period. Most of these in Scotland are located in the south of the country.G. W. S. Barrow, "The childhood of Scottish Christianity: a note on some place-name evidence", in Scottish Studies, 27 (1983), pp. 1–15. From the fifth and sixth centuries, inscribed stones indicate Christianity through their dedications and are spread across southern Scotland. The earliest is the so-called Latinus stone of Whithorn, dating to .J. E. Fraser, From Caledonia to Pictland: Scotland to 795 (Edinburgh: Edinburgh University Press, 2009), , p. 89. In the east and north, Class II Pictish stones began to show Christian symbolism from the early eighth century.B. Webster, Medieval Scotland: the Making of an Identity (New York City, NY: St. Martin's Press, 1997), , p. 55.

Early church buildings may originally have been wooden, like that excavated at Whithorn,J. R. Hume, Scotland's Best Churches (Edinburgh: Edinburgh University Press, 2005), , p. 1. but of those for which evidence survives from this era are basic masonry-built churches, beginning on the west coast and islands and spreading south and east.I. Maxwell, A History of Scotland’s Masonry Construction in P. Wilson, ed., Building with Scottish Stone (Edinburgh: Arcamedia, 2005), , pp. 22–3. Early chapels tended to have square ended converging walls, similar to Irish chapels of this period.T. W. West, Discovering Scottish Architecture (Botley: Osprey, 1985), , p. 8. Medieval parish church architecture in Scotland was typically much less elaborate than in England, with many churches remaining simple oblongs, without transepts and aisles, and often without towers. In the Highlands they were often even simpler, many built of rubble masonry and sometimes indistinguishable from the outside from houses or farm buildings.I. D. Whyte and K. A. Whyte, The Changing Scottish Landscape, 1500–1800 (London: Taylor & Francis, 1991), , p. 117.

Celtic Christianity