Abstract. This paper discusses methodological strategies for architecting ontologies. The development context is an EC IST project, aimed at the use of ontology to help detect and prevent financial frauds. The ontology engineering in this context faces challenges of the scalability of ontology, its applicability in multiple applications, its semantic consistency and comprehensiveness, among others. The paper discusses architecting strategies: layering and modularizing with design patterns, used in producing topical ontologies of fraud and VAT.