The FRBR model is by many considered to be an important contribution to the next generation of bibliographic catalogues, but a major challenge for the library community is how to use this model on already existing MARC-based bibliographic catalogues. This problem requires a solution for the interpretation and conversion of MARC records, and a tool for this kind of conversion is developed as a part of the Norwegian BIBSYS FRBR project. The tool is based on a systematic approach to the interpretation and conversion process and is designed to be adaptable to the rules applied in different catalogues.