Dendrochronological research in North-Central Europe and the East Mediterranean has produced networks of long regional oak (Quercus sp.) reference chronologies that have been instrumental in dating, provenancing, and paleoclimate research applications. However, until now these two important tree-ring networks have not been successfully linked. Oak forests and historical/archaeological sites in southeastern Europe provide the key for linking the North-Central European and East Mediterranean tree-ring networks, but previous dendrochronological research in this region has been largely absent. This article presents the initial results of a project, in which we have built oak tree-ring chronologies from forest sites and historical/archaeological sites along a north-south transect between Poland and northwestern Turkey, with the aim of linking the North-Central European and East Mediterranean tree-ring networks and creating a new pan-European oak data set for dendrochronological dating and paleoclimatic reconstruction. Correlation among tree-ring chronologies and the spatial distribution of their teleconnections are evaluated. The southeastern European chronologies provide a solid bridge between both major European dendrochronological networks. The results indicate that a dense network of chronologies is the key for bridging spatial and temporal gaps in tree-ring records. Dendrochronological sampling should be intensively continued in southeastern Europe because resources for building long oak chronologies in the region are rapidly disappearing.