This study was realised within the scope of an international project launched by the statistical bureau of the European Commission and the Organisation for Economic Co-operation and Development. In Belgium this project was coordinated at the federal level by the Belgian Science Policy Office with input from the regions. In the Flemish Region we were able to make use of the HFFR database of the ECOOM centre at Ghent University. In the Walloon and Brussels-Capital Region we were able to rely on the data of the CREF. The researchers of the ECOOM centre have also contributed to this study with several chapters.