The concept of transnational territories for policy implementation (TTPI) is increasingly presented within the European Union (EU) as offering prospects for tackling common development issues affecting transnational spaces. Following on from the experiences of Interreg-B and the EU macro-regional strategies (MRS), this paper explores the advantages for a transnational territorial development approach and details concrete criteria to delimit those territories worldwide. These are divided into natural geographical elements and human-related geographical features. It concludes that natural elements will prevail when delimiting TTPI, but additional human development layers should be considered in this delimitation process.