The history of popular religion in Scotland includes all forms of the formal theology and structures of institutional religion,Richard W. Santana, Gregory Erickson, Religion and Popular Culture: Rescripting the Sacred (London: McFarland, 2008), , p. 4. between the earliest times of human occupation of what is now Scotland and the present day. Very little is known about religion in Scotland before the arrival of Christianity. It is generally presumed to have resembled Celtic polytheism and there is evidence of the worship of spirits and wells. The Christianisation of Scotland was carried out by Irish-Scots missionaries and to a lesser extent those from Rome and England, from the sixth century. Elements of paganism survived into the Christian era (see: folk religion). The earliest evidence of religious practice is heavily biased toward monastic life. Priests carried out baptisms, masses and burials, prayed for the dead and offered sermons. The church dictated moral and legal matters and impinged on other elements of everyday life through its rules on fasting, diet, the slaughter of animals and rules on purity and ritual cleansing. One of the main features of Medieval Scotland was the Cult of Saints, with shrines devoted to local and national figures, including St Andrew, and the establishment of pilgrimage routes (see: folk saints). Scots also played a major role in the Crusades. Historians have discerned a decline of monastic life in the late medieval period. In contrast, the burghs saw the flourishing of mendicant orders of friars in the later fifteenth century. As the doctrine of Purgatory gained importance the number of chapelries, priests and masses for the dead within parish churches grew rapidly. New "international" cults of devotion connected with Jesus and the Virgin Mary began to reach Scotland in the fifteenth century. Heresy, in the form of Lollardry, began to reach Scotland from England and Bohemia in the early fifteenth century, but did not achieve a significant following.

The Reformation, carried out in Scotland in the mid-sixteenth century and heavily influenced by Calvinism, amounted to a revolution in religious practice. Sermons were now the focus of worship. The Witchcraft Act 1563 made witchcraft, or consulting with witches, capital crimes. There were major series of trials in 1590–91, 1597, 1628–31, 1649–50 and 1661–62. Prosecutions began to decline as trials were more tightly controlled by the judiciary and government, torture was more sparingly used and standards of evidence were raised. Seventy-five per cent of the accused were women and modern estimates indicate that over 1,500 persons were executed across the whole period. Scottish Protestantism in the seventeenth century was highly focused on the Bible, which was seen as infallible and the major source of moral authority. In the mid-seventeenth century Scottish Presbyterian worship took the form it was to maintain until the liturgical revival of the nineteenth century with the adoption of the Westminster Directory in 1643. The seventeenth century saw the high-water mark of kirk discipline, with kirk sessions able to apply religious sanctions, such as excommunication and denial of baptism, to enforce godly behaviour and obedience. Kirk sessions also had an administrative burden in the system of poor relief and a major role in education. In the eighteenth century there were a series of reforms in church music. Communion was the central occasion of the church, conducted at most once a year, sometimes in outdoor holy fairs.

Industrialisation, urbanisation and the Disruption of 1843 all undermined the tradition of parish schools. Attempts to supplement the parish system included Sunday schools. By the 1830s and 1840s these had widened to include mission schools, ragged schools, Bible societies and improvement classes. After the Great Disruption in 1843, the control of relief was removed from the church and given to parochial boards. The temperance movement was imported from America and by 1850 it had become a central theme in the missionary campaign to the working classes. Church attendance in all denominations declined after World War I. It increased in the 1950s as a result of revivalist preaching campaigns, particularly the 1955 tour by Billy Graham, and returned to almost pre-war levels. From this point there was a steady decline that accelerated in the 1960s. Sectarianism became a serious problem in the twentieth century. This was most marked in Glasgow in the traditionally Roman Catholic team, Celtic, and the traditionally Protestant team, Rangers. Relations between Scotland's churches steadily improved during the second half of the twentieth century and there were several initiatives for cooperation, recognition and union. The foundation of the ecumenical Iona Community in 1938 led to a highly influential form of music, which was used across Britain and the US. The Dunblane consultations in 1961–69 resulted in the British "Hymn Explosion" of the 1960s, which produced multiple collections of new hymns. In recent years other religions have established a presence in Scotland, mainly through immigration, including Islam, Hinduism, Buddhism and Sikhism. Other minority faiths include the Baháʼí Faith and small Neopagan groups. There are also various organisations which actively promote humanism and secularism.

Pre-Christian religion

Very little is known about religion in Scotland before the arrival of Christianity. The lack of native written sources among the Picts means that it can only be judged from parallels elsewhere, occasional surviving archaeological evidence and hostile accounts of later Christian writers. It is generally presumed to have resembled Celtic polytheism. The names of more than two hundred Celtic deities have been noted, some of which, like Lugh, The Dagda and The Morrigan, come from later Irish mythology, whilst others, like Teutates, Taranis and Cernunnos, come from evidence from Gaul.B. Cunliffe, The Ancient Celts (Oxford, 1997), , p. 184. The Celtic pagans constructed temples and shrines to venerate these gods, something they did through votive offerings and performing sacrifices, possibly including human sacrifice. According to Greek and Roman accounts, in Gaul, Britain and Ireland, there was a priestly caste of "magico-religious specialists" known as the druids, although very little is definitely known about them.R. Hutton, Blood and Mistletoe: The History of the Druids in Britain (Yale University Press, 2009), , p. 17. Irish legends about the origin of the Picts and stories from the life of St. Ninian, associate the Picts with druids. The Picts are also associated in Christian writing with "demon" worship and one story concerning St. Columba has him exorcising a demon from a well in Pictland, suggesting that the worship of well spirits was a feature of Pictish paganism. Roman mentions of the worship of the Goddess Minerva at wells, and a Pictish stone associated with a well near Dunvegan Castle on Skye, have been taken to support this case.P. Dunbavin, Picts and Ancient Britons: an Exploration of Pictish Origins (Third Millennium Publishing, 1998), , p. 41.

Early Middle Ages

The Christianisation of Scotland was carried out by Irish-Scots missionaries and to a lesser extent those from Rome and England from the sixth century.R. A. Fletcher, The Barbarian Conversion: From Paganism to Christianity (University of California Press, 1999), , pp. 231–3. This movement is traditionally associated with the figures of St Ninian, St Kentigern and St Columba.R. A. Fletcher, The Barbarian Conversion: from Paganism to Christianity (Berkeley CA: University of California Press, 1999), , pp. 79–80.T. O. Clancy, "The real St Ninian", The Innes Review, 52 (2001). Elements of paganism survived into the Christian era. Sacred wells and springs became venerated as sites of pilgrimage.

Most evidence of Christian practice comes from monks and is heavily biased towards monastic life. From this can be seen the daily cycle of prayers and the celebration of the Mass. Less well recorded, but as significant, was the role of bishops and their clergy. Bishops dealt with the leaders of the tuath, ordained clergy and consecrated churches. They also had responsibilities for the poor, hungry, prisoners, widows and orphans. Priests carried out baptisms, masses and burials. They also prayed for the dead and offered sermons. They anointed the sick with oil, brought communion to the dying and administered penance to sinners. The church encouraged alms giving and hospitality. It also dictated in moral and legal matters, including marriage and inheritance. It also impinged on other elements of everyday life through its rules on fasting, diet, the slaughter of animals and rules on purity and ritual cleansing.

Early local churches were widespread, but since they were largely made of wood,G. Markus, "Religious life: early medieval", in M. Lynch, ed., The Oxford Companion to Scottish History (Oxford: Oxford University Press, 2001), , pp. 509–10. like that excavated at Whithorn,J. R. Hume, Scotland's Best Churches (Edinburgh: Edinburgh University Press, 2005), , p. 1. the only evidence that survives for most is in place names that contain words for church, including cill, both, eccles and annat, but others are indicated by stone crosses and Christian burials. Beginning on the west coast and islands and spreading south and east, these were replaced with basic masonry-built buildings. Many of these were built by local lords for their tenants and followers, but often retaining a close relationship with monastic institutions.I. Maxwell, A History of Scotland's Masonry Construction in P. Wilson, ed., Building with Scottish Stone (Edinburgh: Arcamedia, 2005), , pp. 22–3.

Viking raids began on monasteries like Iona and Lindisfarne began in the eighth century. Orkney, Shetland and the Western Isles eventually fell to the Norsemen.W. E. Burns, A Brief History of Great Britain (Infobase Publishing, 2009), , pp. 44–5. Although there is evidence of varying burial rites practised by Norse settlers in Scotland, such as grave goods found on Colonsay and Westray, there is little that enables a confirmation that the Norse gods were venerated prior to the reintroduction of Christianity.J. Jensen, "The Norse gods in Scotland" in A. Woolf, ed., Scandinavian Scotland – Twenty Years After (St Andrews: St Andrews University Press), pp. 52 and 58. The Odin Stone has been used as evidence of Odinic beliefs and practices but the derivation may well be from "oathing stone".J. Jensen, "The Norse gods in Scotland" in A. Woolf, ed., Scandinavian Scotland – Twenty Years After (St Andrews: St Andrews University Press), p. 54. A few Scandinavian poetic references suggest that Orcadian audiences understood elements of the Norse pantheon, although this is hardly conclusive proof of active beliefs.J. Jensen, "The Norse gods in Scotland" in A. Woolf, ed., Scandinavian Scotland – Twenty Years After (St Andrews: St Andrews University Press), pp. 54 and 59. Nonetheless, it is likely that pagan practices existed in early Scandinavian Scotland.J. Jensen, "The Norse gods in Scotland" in A. Woolf, ed., Scandinavian Scotland – Twenty Years After (St Andrews: St Andrews University Press), , p. 62.

High Middle Ages