This paper investigates the factors governing the distribution of ge- in the German past participle (ge-bildet, unter-ge-gangen). The claim is that ge- belongs to the morphophonological class of inseparable verbal prefixes and that all distributional facts of ge- follow from this fact. The distinctive properties of this class are the following. First, only the last potentially free stem is prefixed. Second, an adjacent stressed syllable is obligatory. Third, at most one element of this class is allowed in a word. The diachronic development of ge- plays an important role in the analysis. It is shown that prefixed verbs lack ge- due to semantic and diachronic reasons. The stress criterion that is always mentioned in accounts of the distribution of ge- gets a new assessment in light of comparative data from Dutch, Afrikaans, New and Middle High German. Data from German dialects are also discussed. The analysis is carried out in the framework of Optimality Theory and defended against Neef (1996) and Geilfuß-Wolfgang (1998).