This book provides theoretical and practical insights into city modelling from a geomatics perspective. It offers a critical discussion of state-of-the-art solutions for the geometric and semantic generation of 3D city models, their management and maintenance in GIS environments, and also their representation and visualization. In addition it also provides examples of real-world applications with two successful applications of city model databases used at national level. 3D and 4D (space and time) city modelling emanates from advances in the creation and use of 2D maps and through technical developments using database management systems to the point where a city model actually becomes the main geometrical unit of a 3D geographical information system (GIS) environment. 3D spatial queries open up new horizons for many application areas, such as ecosystem modelling and simulations, integration of indoor data with the help of building information models (BIM), etc. Furthermore, semantic information associated with the 3D data enables spatiotemporal querying and analysis. 3D city models and GIS empower the smart city concepts and are inevitably crucial for smart management of cities in which the majority of humans live. This increasing trend to implement 3D city models and monitor/store their changes in time in a 3D GIS environment has brought the need for more studies of every stage in their production, management and presentation. These stages range from data collection and processing to 3D object reconstruction and model generation, spatial and non-spatial data management, and representation. With chapters contributed by internationally recognized experts 3D/4D City Modelling provides a broad overview of the different aspects of the subject and brings together the theoretical information and best practices that comprise the major components of the city modelling process. It synthesises the technological and methodological advancements in geospatial information science and geoinformatics with special focus on 3D city models.