Summary: We describe the Zinc modelling language. Zinc provides set constraints, user defined types, constrained types, and polymorphic predicates and functions. The last allows Zinc to be readily extended to different application domains by user-defined libraries. Zinc is designed to support a modelling methodology in which the same conceptual model can be automatically mapped into different design models, thus allowing modellers to easily “plug and play” with different solving techniques and so choose the most appropriate for that problem.