Past trade in oak from the lands to the east and south of the Baltic Sea was extraordinary in that it dominated the Northern European market for specialized oak products for many centuries. Equally extraordinary is the fact that since the 1980s, when a large corpus of dendrochronological data from artworks was demonstrated to represent the material evidence for this past trade, we, until now, have not been able to pinpoint where, in this large region, the trees for this trade grew. Through our analysis we can now present the likely sources of three major timber groups in this material, and significantly, the new chronologies that we make available here, will be the key foundation for dating and identifying provenance of Baltic oak, for tree-ring research long into the future.