The number of people incarcerated in many European countries has increased over the course of recent years. This trend has made the number of prisoners exceed the number of places available for them. Much research focuses on the identification of variables that explain the ups and downs in the use of imprisonment, such as sociological or ideological factors. This research analyzes the increase in imprisonment by comparing two German Lander (Federal States) that experienced the largest and smallest growth between 1990 and 1998, respectively. The analysis was based on official criminal justice statistics. Results show that it was the number of people receiving a criminal sentence and the number of people remanded in custody that were the most likely explanations for the increase in imprisonment figures in these two States, Lower Saxony and Schleswig-Holstein. The quantitative developments in the number of people identified by the police only partially contributed to the problem. The comparison between the two Lander demonstrates that the largest cause of the problem can be attributed to accusation and sentencing decisions. This is consistent with findings from the literature on the explanation of imprisonment figures in other countries. Across different offense types, Lower Saxony accused and sentenced more people in general and to conditional and unconditional prison terms in particular. The differences were especially pronounced with violent offenses. These factors are consistent with other European literature on prison overcrowding. A multi-method, detailed investigation of several factors like crime, prosecutorial selection, sentencing, reconviction, and early release is required in searching for causes of rising imprisonment figures. 5 figures, 4 notes, 40 references