A methodology for object-oriented (OO) system development is introduced. Its relevance is illustrated by an ongoing project in the banking sector. This project failed initially while following a traditional life-cycle-oriented approach. We identify three main features that made the second OO phase successful—employing OO techniques; combining these techniques with a guideline, the tools-and-materials metaphor; and employing the concepts of evolutionary system development. We base our approach to object orientation on the language used in the application domain, thereby unifying analysis, design, and software construction. The tools-and-materials metaphor helps to bridge the gap between application-oriented and technical models as it starts with identifying the relevant means and objects of work in the application domain, thereby providing a guideline for constructing interactive systems. As we view system development essentially as a learning-and-communication process, evolutionary system development—with its feedback cycles among the parties involved and the use of prototyping—is the key to making the software process a success. The underlying idea of our OO approach is that it not only allows concepts of the application domain to be mapped directly onto to a technical model, but, foremost, it provides techniques, strategies, and appropriate document types supporting the continuous communication between all parties involved in the development process of software systems.