The COST Action FP1304, known as PROFOUND (“Towards Robust Projections of European Forests Under Climate Change”), was a research initiative that operated from May 13, 2014, to May 12, 2018. This interdisciplinary network aimed to enhance the reliability of projections concerning European forest ecosystems in the face of climate change. It addressed key challenges such as the lack of harmonized large-scale datasets and the need for robust methods in model parameterization, evaluation, and comparison. PROFOUND’s objectives included harmonizing European forest data, comparing various forest modeling approaches, developing standards for model calibration and evaluation, and facilitating probabilistic multi-model projections under changing climatic conditions. The outcomes of this action have significantly contributed to integrating forest modelers and data experts across Europe, providing decision-makers with more dependable information regarding model prediction uncertainties. A notable achievement of PROFOUND is the development of the PROFOUND Database (PROFOUND DB), which offers a comprehensive collection of empirical data on European forests. This database is designed to calibrate and evaluate vegetation models that simulate climate impacts at the forest stand scale. It encompasses a wide array of data, including site descriptions, soil characteristics, climate data, atmospheric CO₂ levels, nitrogen deposition, tree and stand-level information, and remote sensing data for nine diverse forest stands across Europe. For five of these sites, the database also provides time series data on carbon fluxes, energy balances, and soil water content. Additionally, the PROFOUND DB includes climate and nitrogen deposition datasets covering historical periods and various future climate change scenarios based on Representative Concentration Pathways (RCPs). This resource is freely accessible and can be utilized via the ProfoundData R package, which offers functions to explore, visualize, and extract data for model setup, calibration, and evaluation. The collaborative efforts of PROFOUND have been instrumental in advancing the understanding of how European forests may respond to environmental changes, thereby aiding in the development of effective strategies for forest management and conservation in a changing climate.