There has been significant recent interest, within the aspect-oriented softwaredevelopment (AOSD) community, in representing crosscutting concerns at various stages of thesoftware lifecycle. However, most of these efforts have concentrated on the design andimplementation phases. The focus of this paper is on representing aspects during requirementsmodelling. In particular, the issue of how to model aspects as part of scenario-based modelling isaddressed. The use of scenarios is common in requirements development and analysis. The authorsdescribe how to represent and compose aspects at the scenario level. Aspectual scenarios aremodelled as interaction pattern specifications (IPSs) and are composed with nonaspectual scenariosusing instantiation and special composition operators. The composed collection of scenarios canthen be translated automatically into a set of state machines using an existing state machinesynthesis algorithm. The resulting set of state machines is an executable form of the scenarios andcan be used for simulation and analysis of the requirements.