We have worked with the construction and use of 3D city models for about ten years. This work has given us valuable experience concerning model methodology. In addition to this collection of knowledge, our perception of the concept of city models has changed radically. In order to explain this shift in paradigms we begin by describing some of the concrete models we have made, showing the relationship between model structure (methodology and content) and model use. We also describe the projects we are working on at present in order to illustrate new ideas concerning the potential development of 3D city models.