Data warehouses (DWs) have become one of the largest investments in the past years for organisations, and incorporating external data into a DW can give organisations huge possibilities. Organisations that successfully manage to incorporate external data into a DW have an advantage over those who do not, but there are problems with incorporating data acquired from outside the organisation, and there is a lack of research aimed at these problems. The comprehensive aim of this dissertation is to characterise and categorise problems with incorporating external data. The available literature was scanned to find problems and an interview study was conducted to validate the problems found in the literature. Respondents from five well-known organisations in Sweden participated and the result is a list of problems backed up by both literature and empirical findings