The goal of the WikiVienna project is the creation and update of a large 3D urban model from a continuously expanding set of images. The idea of the Wikipedia project is borrowed, where everybody can contribute to increase the amount of information. However, in this project a spatial information layer to organize the data is added and mobile devices are used as interfaces to this information space. In order to create 3D models from an unordered set of images, different computer vision methods are needed. This ranges from camera calibration to wide baseline matching and area-based depth estimation algorithms. The main challenge is to build a robust system which works fully automated for various cameras (e.g. mobile phone cameras) and in different environments. The reconstructed 3D city model can then be used for many applications ranging from tourism and cultural heritage over city planning to emergency support.