Building useful representations of reality, particularly of key features and relationships (and even though models may be complex they are simpler than reality). Models can be informal (mental models) or formal (computational models). Key roles of modelling are to provide a) representations and understanding of systems, including complex systems, b) tools for understanding and managing unknowns, c) tools for decision support, d) participatory processes that expose diversity (eg differences in mental models) and e) tools for integration (eg of different knowledge and perspectives).