The Polish-German borderland provides a test of whether territorial cooperation follows actual economic linkages or merely geographical proximity. The chapter combines literature and legal-document reviews with Eurostat GDP data for NUTS3 border regions from 2000 to 2020. Cyclical fluctuations are extracted with the Hodrick–Prescott filter and compared through Pearson correlations. Although local governments frequently cooperate with directly adjacent partners, business-cycle convergence between neighbouring Polish and German border regions is rare and usually weak. Some correlations appear between territories that do not share a border, while several commonly cited cross-border links show little economic synchronisation. The chapter challenges border-centred thinking in cooperation policy. More effective projects require evidence on real socio-economic interdependencies, not only administrative adjacency or historical partnership patterns.