The recent years observe the vast development in new techniques and methods for modelling, visualization, and analysis of 3D digital cities, as the need of digital twins of urban environment in different applications and simulations has been increased dramatically. This special issue attempts to give an overview of the recent progress and future tendency of research activities in the aforementioned domain. The special issue includes seven articles with topics ranging from data acquisition and data processing, to data modelling and applications. The experience in this special issue says that 3D building models should contain semantic information for various applications and therefore set the corresponding requirement in techniques and methods for 3D objects detection and modelling.@en