More than a quarter of people in Scotland say they do not follow any religion, according to new figures.
The latest census shows that two-thirds consider themselves Christian, with 42% regarding themselves as Church of Scotland and 16% as Catholic.
Islam is the second-largest religious grouping - despite Muslims accounting for less than 1% of the population.
Buddhists, Hindus, Jews and Sikhs made up less than 2% of the population, says an analysis of the 2001 census.
The census that year included questions on religion for the first time.
A total of 28% of people in Scotland said they had no religion, while 65% identified themselves as Christian.
More than 2.1 million people said they were Church of Scotland and 803,700 Catholics.
Fall-off
The census showed their were 42,600 Muslims, 6,800 Buddhists, 5,600 Hindus, 6,400 Jews, and 6,600 Sikhs.
The Church of Scotland saw the biggest fall-off in religious affiliation over the years.
While more than 47% of people said they had been brought up as Church of Scotland, just 42% still had that affiliation.
This differential of nearly five per cent was the biggest of all the religions. Among Roman Catholics, the difference was just over one per cent and for all the non-Christian groupings it was well under one per cent.
Census findings from elsewhere in the UK suggest more people in England and Wales (77%) and Northern Ireland (86%) regard themselves as having a religion, compared to 65% in Scotland.
But the Scottish Executive statisticians said this could be due to differences in the format of questions south of the border.
They also said these figures were probably comparable with the Scottish question on religion of upbringing, which showed 74% saying they had been brought up in a faith.
The figures showed Muslims had the youngest age profile, with 31% aged under 16 years.
Minority religion groups tend to be concentrated in Glasgow and Edinburgh, with nearly half - 49% - of Scotland's Jewish population living in East Renfrewshire.
Two-thirds of Muslims consider themselves to be of Pakistani origin, while 86% of Sikhs and 82% of Hindus consider themselves of Indian origin.
About 42% of Sikhs and 39% of Muslims in the 16-74 age group have no qualifications, compared with 33% for all people in Scotland in that age group.
The Muslim unemployment rate is highest at 13%, or double the overall Scottish rate.
The Church of Scotland has an older age profile than Roman Catholics, with about 45% over 50, compared to 32% of Roman Catholics.
Roman Catholic families are also more likely to have dependent children (48%) than the Church of Scotland group (36%) and to live in large urban areas - 54% compared to 33% for the Church of Scotland.