We describe a set of modules that together make up a grapheme-to-phoneme coversion system for Dutch. Modules include a syllabification program, a fast morphological parser, a lexical database, a phonological knowledge base, transliteration rules, and phonological rules. Knowledge and procedures were implemented object-orientedly. We contrast GRAFON to recent pattern recognition and rule-compiler approaches and try to show that the first fails for languages with concatenative compounding (like Dutch, German, and Scandinavian languages) while the second lacks the flexibility to model different phonological theories. It is claimed that syllables (and not graphemes/phonemes or morphemes) should be central units in a rule-based phonemisation algorithm. Furthermore, the architecture of GRAFON and its user interface make it ideally suited as a rule-testing tool for phonologists.