The Integrated Employment Biographies (IEB), provided by the IAB, can be supposed to become one of the most important data sources for labour market research in Germany: The IEB link process data information of the Federal Employment Agency on periods of job search, benefit reception and participation in labor market measures with reports on employment periods. However, on the one hand the IEB require researchers to make assumptions about the data generation process, since unexpected overlaps between episodes are observed to some degree. On the other hand, the data provide only an incomplete picture of labor market careers - gaps between episodes may for instance result from periods of schooling, home work or self employment. Taking into account the importance of the data base it is sensible to provide standards in addressing the treatment of these problems. The current project is devoted to this issue regarding one of the key variables: The duration of unemployment. The project thus includes a critical discussion of the question of defining employment. Finally, sensitivity analyses should give an impression, whether and how much corrections and classifications of the IEB affect the results of labour market research in different areas.