The GeoTwinn is the Horizon 2020 Twinning project funded by European Commission and is fully entitled: Strengthening research in the Croatian Geological Survey: Geoscience-Twinning to develop state-of-the-art subsurface modelling capability and scientific impact. The project twins the Croatian Geological Survey (HGI-CGS) with two world-leading geoscience research institutions: the Geological Survey of Denmark and Greenland (GEUS) and the British Geological Survey of the United Kingdom Research and Innovation (BGS-UKRI). The Project has started in October 2018, and is coordinated by HGI-CGS. The major aims of the project are: to significantly strengthen HGI-CGS’s research potential and capability, networking between scientists and institutions, and also development of ideas and new projects proposals. During three years of implementation, HGI-CGS experts will have the opportunity to collaborate with eminent sci-entists from other two partnering institutions. HGI-CGS will also benefit from a range of research tools, technologies, software and methods at the disposal of GEUS and BGS-UKRI. Almost thirty scientists from HGI-CGS will participate in the training programme which includes intensive training, consultations, and application of gained knowledge on test areas/data. The program involves short term visits, two-way scientific exchanges and workshops which will support HGI-CGS to strengthen research and capabilities in four important geoscience subject areas (Fig. 1): (1) 3D geological surveying and modelling (WP1) – to em-bed state-of-the-art geological surveying, interpretation and modelling. In the first activity, modern digital geological workflow and subsurface modelling capabilities including 3D virtual reconnaissance will be introduced. Also, digital field data capture, geological databases and 3D geological modelling are introduced. The second activity will reinforce these 3D visualisation and modelling skills by applying them to pilot areas using deep seismic reflection and borehole data. (2) advanced groundwater flow and contaminant transport modelling (WP2) – to understand, simulate and predict the movement of groundwater and contaminants in the subsurface. It comprises two activities, the first of which deals with strengthening HGI-CGS’s capacity to undertake cutting-edge numerical groundwater flow in porous aquifers, incorporating the robust assessment of uncertainty. The second activity deals with groundwater flow in the karst aquifers of Dinaric karst region of Croatia using advanced statistical time-series analysis methods. It will also introduce research methods to identify and analyse emerging groundwater contaminants. (3) identification and analysis of geohazards (WP3) – to introduce cutting-edge remote sensing methods for hazardous geological processes detection, monitoring and analysis. Training also includes the interpretation and visualisation of stereo imagery, processing of satellite imagery, INSAR interferometry and satellite detection of small-scale movements. The project also contains training on heuristic, statistical and geostatistical techniques to enable production of landslide susceptibility mapping. (4) geothermal energy (WP4) – scientific exchanges and training that will lead to new research into geological controls on subsurface heat flow and geochemical processes operating in hydrothermal systems. HGI-CGS staff will attend training on sampling and analytical methods of noble and dissolved gases from hydro-thermal systems. The training is also directed toward interpretation of hydrochemical data and geochemical modelling of hydrothermal systems. Second segment of the training develops fluid and heat flow modelling capability through numerical modelling of geothermal systems.The project will increase the research capacity, excellence and skill of the coordinating partner whilst fostering a network of both early career and more experienced researchers who can collaborate to produce high quality and impactful results: • a step-change in the excellence and impact of the re-search published HGI-CGS staff; • raise the reputation and the research profile of HGI-CGS scientists for novel research; • enhance research and innovation related to environmental issues, including the need for a shift to a low-carbon economy, climate change adaptation and risk management, and environmental protection and resource efficiency; • write successful bids into EU and other research grant schemes; • develop and enhance network of collaborators across the European Union; • form partnerships between the participating organisations, that outlast the project. Whilst the project focuses on supporting HGI-CGS to achieve a step-change in its research capacity, and the research profile of its scientists, it also offers significant benefits to GEUS and BGS-UKRI. By exposing GEUS and BGS-UKRI staff to a diverse range of geological set-tings within Croatia, particular environmental challenges, and to a different, large group of stakeholders, partnering institutions will also increase their level of expertise and knowledge.