CityGML is considered an optimal standard for the representation of 3D city models. However, due to its complex structure, easy-to–use data retrieval is important, in terms of interoperability. This implies choosing the implementation of Web Service Technologies and in particular the WFS, as the most suitable OGC standard for retrieving the real geometry data. Nevertheless, this standard serves data mainly based on their geometry, while CityGML also covers topology and more importantly semantic aspects of 3D city models. Therefore, this paper examines and presents the new CityGML RESTful Web service, instead of the OGC WFS. This Web Service is conceptually designed to achieve CityGML data retrieval based on their semantics characteristics. In this context, several principles and guidelines of the new CityGML RESTful Web service are described and the “CityModels” resource is presented. Additionally, the conceptual design of the bldg resource and its child resources based on the level of details is also presented.