Climate change and biodiversity loss create a fundamental challenge for forests and the ecosystem services they provide for societies. These challenges create a critical demand for large-scale data on the structure and composition of forest ecosystems for both cutting edge research and policy-driven monitoring efforts at EU level. While National Forest Inventories (NFIs) provide this information, they are carried out with different sampling designs in each country. This threatens the comparability of the quantification of forest structure and composition between countries. Thus, the INSTRUCT project evaluates and develops methods for the quantification from diverse sources of ground-based data available at large scales. The project uses advanced statistical methods to enable analyses across various data sources. The development is done in international collaboration with researchers in forest sciences, biodiversity, and statistical analyses.