As the European Union grows together we are faced with an increasing number of European surveys and statistics that rely on national instruments or questionnaires. We lack valid instruments with functional equivalence that allow international comparative analysis. This problem is especially important in the case of demographic and socio-economic variables. The usual practice in comparative social research is to work with national questionnaires and classifications thereby making meaningful comparisons questionable. To overcome these problems this book offers rules of comparison, tested instruments and examples for the measurements of basic demographic and socio-economic variables. The book consists of five parts and a concluding chapter.