This Thesis sets out to examine in its eighteenth century context a Scottish Calvinist sectarian group of churches deriving the main features of their faith and practice from the writings of John Glas and Robert Sandeman. It proceeds by way of a description of the milieu out of which they came to describe the birth and spread in Scotland of these groups, the Glassites, the Scotch Baptists and the Old Scots Independents, and a similar group, the Bereans. Using some manuscript evidence and other sources, it looks at the social origin of the churches, and the composition of the groups. Some main theological distinctives are outlined, and the social and religious life of the groups illustrated, from contemporary sources. With this material as the evidence, an attempt is made to place the group in a wider setting, by comparison with other sectarian movements, and the conclusion drawn that the eighteenth century Independent movement in Scotland can be classified as a variety of the Revolutionary type of Sect, although other characteristics occur. That both social change and deeply held theological and ecelesiological beliefs contributed to the special shape of the groups is demonstrated.