We present the first European network of tree ring δ¹³C and δ¹⁸O, containing 23 sites from Finland to Morocco. Common climate signals are found over broad climatic-ecological ranges. In temperate regions we find positive correlations with summer maximum temperatures and negative correlations with summer precipitation and Palmer Drought Severity Indices (PDSI) with no obvious speciesspecific differences. Regional δ¹³C and δ¹⁸O chronologies share high common variance in year-to-year variations. Long-term variations, however, exhibit differences that may reflect spatial variability in environmental forcings, age trends and/or plant physiological responses to increasing atmospheric CO₂ concentration. Rotated principal component analysis (RPCA) and climate field correlations enable the identification of four sub-regions in the δ¹⁸O network - northern and eastern Central Europe, Scandinavia and the western Mediterranean. Regional patterns in the δ¹³C network are less clear and are timescale dependent. Our results indicate that future reconstruction efforts should concentrate on δ¹⁸O data in the identified European regions.