[en] Managing radioactive waste inventories is much like managing huge amounts of technical and scientific data. Most of these data are aimed at one common goal: the knowledge of the radiological and chemical contents of a radioactive waste package destined to be disposed of in a final repository. All calculations concerning the design of such a repository, be it performance assessments or safety evaluations or, quite plainly, its dimensions, require a whole range of data, the most important being the number of primary waste packages that will exist at the end of the nuclear program and their radionuclide contents and chemical composition. Assessing these data involves a lot of number crunching. The pillars of the knowledge of these data are twofold, namely an acceptance system and an inventory of radioactive waste. Both are part of the radioactive waste management system put in place by ONDRAF/NIRAS, the Belgian agency for radioactive waste and enriched fissile materials. This paper outlines the way the acceptance system interacts with the inventory of radioactive waste. It then focuses on the inventory itself, describing the methodology and giving some of the key results of the most recent inventory exercise completed in 2003. The final paragraph highlights the way this inventory is used as an integrated part of a low-level waste management system. (author)