ABSTRACTEgon Hartmann (1919–2009) was a prominent East German planner and a rising star of the architectural scene in the early years of the German Democratic Republic (GDR). A graduate from the College for Architecture and Fine Arts, he became Chief Architect of Thuringia in 1951 and built such remarkable architectures like the government high-rise in Erfurt. Nevertheless, he left the GDR in 1954, settled in West Germany where he first worked in Mainz and then moved to Munich and thereby became a ‘crosser’, one of the few planners who successfully worked on both sides of the Iron Curtain. This paper traces Egon Hartmann’s private–professional ties based on the letters sent to/ from him across the inner-German border that have been archived in his estate. It aims to show that integrating a personal dimension and very specific patterns of communication into the analysis of transnational connections, transfers, exchanges, and cooperation of planners reveals rather informal ties that created unexpected relations across the Iron Curtain. Nevertheless, those were a crucial resource for the planners’ career and private life, when formal bonds were destabilized due to large-scale political tensions and the division of the two worlds.