From respectively 1852–1938 and 1863–1897, Guyana and New Caledonia received tens of thousands of men and hundreds of women sentenced to hard labour, deportation or relegation on their soil. This article aims to compare the social history of these two penal colonies, something which has never been done specifically. Transportation and its effects on the populating of both countries are here analysed in context: in the colonial situation experienced by the two territories, in contact with other populations, whether indigenous, imported or colonial. Subjected to the same rural utopia defended by the 1854 act on convict transportation, the two colonies nonetheless evolved very differently. It is this we shall be investigating in a close field study. With this ‘ground level’ approach, we hope to reveal how original colonial societies were formed out of these particular and remarkable penal experiments