In this paper a phoneme-to-grapheme system (PTG) for the German language is introduced. Since this system is based on rules, a dictionary look-up is not required, and thus the conversion of an unrestricted vocabulary is possible. A necessary requirement, however, is a correct segmentation of continuously spoken sentences into isolated words. For the PTG system the phonemic representation of these words must be error-free, i.e., it has to correspond to the standard pronunciation dictionary for German (Duden (ref 1)). Nevertheless, an additional system which allows for reconstructing such a required error-free phoneme word from a non-standard phone code word is still in the process of being developed. Due to the definition of the input and output interface the phoneme-to-grapheme conversion system has to be interpreted as part of a blackboard model which collects and uses all information available on the speech-to-text conversion.