The purpose of this study was to collect data which would facilitate the analysis of segregation and social structure in early twentieth century Belfast in relation to the main religious groups in the city - Catholics, Episcopalians, Presbyterians, Methodists and other Protestant groups. Variables An eight per cent sample of households was drawn from the 1901 Census schedules (Public Record Office, Dublin) and all variables on the form recorded: age, sex, relationship to head,birthplace, religion, occupation, literacy, Irish language. Each sample household was also linked with valuation data from the special valuation of Belfast, 1900-1901, and also with the <i>Belfast and Ulster directory</i> for 1896 and 1906, to discern whether the same family was at the address in those years.