In our article we analyse the role of place names in the construction of national identities in the Czech-Polish borderlands. The analysed cities are Český Těšín, Czechia, and Cieszyn, Poland, cities which were created after the division of the original Austrian Silesian city of Těšín/Cieszyn/Teschen between the newly established states of Czechoslovakia and Poland in 1920. Using official maps, archival documents, interviews, and GIS we analyse the transformations of the toponymic landscape on both sides of the state border during the 20th century, identify principal trends and significant differences in different periods and sides of the border, and show how Austrian, German, Czech, Polish and Silesian nationalism – in competition with each other and with other levels of group identification and other political ideologies – have strategically used place names to promote a clear national identification of the city inhabitants in a region of great historical, ethnic and political complexity.