A computer database of detailed information on 23,753 emigrants who sailed from the port of Derry in the northwest of Ireland was constructed, using Customs and ship passenger records that together spanned the years 1803- 1867, though not continuously. This information was used to trace changes in the origins of the emigrants, their age and sex distribution, their occupational backgrounds, their destinations, and in how they paid for their fare. Analysis showed that that the profile of emigration changed from emigration of mainly young, unattached males in the early part of the century to family migration during the Famine years, subsequently changing to emigration of equal numbers of males and females, mostly as young adults. Major differences found between the emigrant populations who sailed for Canada and the United States respectively were related to the cost of fares and the extent of assistance to emigrate. Pre-paid fares were found to be very significant, especially during the Famine years. Until the early 1860s the majority of the emigrants were from the more affluent, fertile areas of the north-west. Both the pattern of pre-paid fares and the concentration of the emigrants' origins were closely related to the migration tradition within the area. This tradition, dating back to the eighteenth century, helped create a migration mentality, promoted subsequent emigration, and gave rise to the pre-payment of fares by earlier emigrants. Although the Famine had a major impact on the area, it was not the instigator of mass migration from the northwest. The demise of the linen trade and associated economic crises were more important in this respect. The response to population pressure and economic crises varied within the region as well as with time.