The aim of the CityGML Quality Interoperability Experiment was to define data quality requirements for a general CityGML data specification, to provide recommended implementation guidance for 3D data, and to provide a suite of essential quality checking tools to carry out quality assurance on CityGML data. The data requirements and recommended implementation guidance were obtained by experimentation and may serve as input to extend and refine the CityGML standard. These requirements and guidance should meet the OGC Membership and community "thirst" for better implementation guidance for OGC standards, in this case CityGML. The QIE was carried out as a joint activity between OGC, SIG3D and EuroSDR.@en