Effective RE must reconcile the need to achieve separation of concerns with the need to satisfy broadly scoped requirements and constraints. Techniques such as use cases and viewpoints help achieve separation of stakeholders' concerns but ensuring their consistency with global requirements and constraints is largely unsupported. We build on recent work that has emerged from the aspect-oriented programming (AOP) community to propose a general model for aspect oriented requirements engineering (AORE). The model supports separation of crosscutting functional and non-functional properties at the requirements level. We argue that early separation of such crosscutting properties supports effective determination of their mapping and influence on artefacts at later development stages. A realisation of the model based on a case study of a toll collection system is presented.