An approach to information systems development based on systematic complexity reduction is presented. It facilitates integrated specifications and at the same time it provides facilities that allow the developers to split a complicated task into a set of more comprehensible subtasks. Through the introduction of viewspecs the suggested approach recognizes the need to adopt multiple perspectives when developing large and complex information systems. The possibility of using pre-defined filters, user-defined filters and combinations of these, provides the developer using the complexity reduction approach with a great deal of freedom in focusing on different aspects of a system. The viewspecs are used `actively' during the development in the sense that they do not only serve as passive components or projections of a set of specifications (e.g., for presentation purposes) but also serve as a basis for entering new information into specifications.