This paper presents the work in progress of a research project that aims at establishing a reference model for 3D geo-information in the Netherlands. The research project is initiated by four national organizations: 1) Ministry of Housing, Spatial Planning and the Environment, 2) Kadaster, 3) Geonovum, and 4) the Netherlands Geodetic Commission. These four organizations responsible for geo-information in the Netherlands recognized the urgent need for a standardized approach and therefore initiated a 3D pilot. In the 3D pilot, a uniform approach for 3D geo-information modeling is explored in collaboration with a large number of stakeholders ultimately resulting in national agreements and a national standard, extending CityGML, for use of 3D geo-information. The final aim of the 3D pilot is to evoke a breakthrough in the use of 3D geo-information in the Netherlands. In the pilot providers and users of geo-information closely collaborate, which ensures that the providers are familiar with precise requirements of the users. This pilot aims also at an improved accessibility to 3D geo-information and the supporting technologies, which may push advances in 3D applications. The paper will present the scope of the pilot, the methodology and the first results of the investigations with the four working groups. The first working group investigates questions such as generation of a 3D reference model from different data sources, such as point clouds and images from airborne and terrestrial sensors, 2D data from above and below the surface, and 3D models from the building domain (CAD/AEC/BIM/IFC models). The second working group concentrates on defining a 3D standard for the Netherlands, considering international and national developments. The third working group is responsible for organizing of a 3D testbed to study the bottlenecks in organizing the3D information in a database system. The fourth working group investigates the use of 3D geo-information in various applications, with the goal to define and execute appropriate use cases.