This paper deals with definition and assessment of decision criteria for sewer asset management. The work was prepared within a doctoral thesis (Ibrahim, 2008) and is part of a research program (INDIGAU, 2007-2010, www.indigau.fr) supported by the French National Research Agency (ANR). Three main ideas are exposed and illustrated in this paper. 1) Each rehabilitation criterion may be seen as the result of successive aggregations of complementary indicators provided by various methods or sources (visual inspection, O&M data, investigation techniques, etc.) at several spatial scales (sewer segment, catchment). 2) Combining indicators may be computed by means of a limited number of “if ... then ...” rules. The French RERAU method provides 4x4 tables defining how to combine couples of indicators, each one being evaluated on a four-grade ordinal scale (G4 being the highest gravity). 3) The aggregation tables can be converted into fuzzy aggregation rules associated to the use of fuzzy indicators. Compared to crisp data and rules, the use of fuzzy indicators and fuzzy rules provides finer results and improves the robustness of the fusion process.