Requirements engineering is an ill-defined, but growing area of research which addresses a critical problem, that of designing the right thing. This paper reports research on the ESPRIT project NATURE (Novel Theories Underlying Requirements Engineering). A framework for RE research is introduced which covers overall conceptions of the modelling and process views of requirements engineering. Within this framework, current modelling techniques can be reused but are augmented by generic models supporting the reuse of domain knowledge for requirements analysis and validation, and by an enterprise modelling structure emphasising the role of user objectives in requirements engineering. The basic understanding of RE as “establishing visions into context” leads into the NATURE process model that formalises RE activities as freely composable process chunks linked to contexts. The process model is then used to develop roadmaps of pathways for RE activities within the enterprise model structure. This structure also requires a broader definition of viewpoints and their resolution in the RE process. The last part of the paper presents the NATURE Computer Aided Requirements Engineering (CARE) environment, integrated via the ConceptBase repository. It comprises tools for viewpoint an repository management, process guidance, traceability support, and matching tools for reuse, viewpoint integration and validation using similarity and analogical reasoning mechanisms. The tools section also reports critiquing and validation facilities, and schema integration tools. The paper concludes with a review of related work in conceptual modelling and other aspects of Requirements Engineering.