Representative longitudinal data for German firms (establishments or enterprises) that can be used for scientific analyses are mainly from two sources, the IAB Establishment Panel and the AFiD-Panel based on surveys performed by the Statistical Offices. This paper compares the data from these two sources. It is argued that the two types of firm data are complements and not substitutes for empirical economic analyses. Both have specific strengths and weaknesses, and both are well suited to investigate some but not all topics, and some topics cannot be analyzed with one type of data at all. Therefore, both types of data are needed as inputs for empirical economic research.