For the last 25 years European Territorial Cooperation (ETC), known as Interreg, has promoted the harmonious economic, social and territorial development of the EU as a whole. Starting as a community initiative with 11 participating Member States and a budget of 1.1 billion, it has grown to benefit all 28 Member States, with a budget of 10.1 billion euros. Although initially only covering cross-border cooperation, Interreg has expanded to encompass three strands of cooperation: cross-border (Interreg A), transnational (Interreg B) and interregional (Interreg C). Interreg has become a key instrument in supporting and promoting cross-border cooperation across a range of fields including health, education and transport. Interreg A (cross-border cooperation) supports cooperation between adjacent NUTS III border regions in at least two different EU Member States or between EU Member States and some countries outside the EU. It aims to develop the untapped growth potential of border areas, as well as enhancing cooperation to support the harmonious development of the Union. The EU includes substantial border regions: 37.5% of the EU population live in the border areas defined by 38 international borders. Borders often represent barriers to harmonious development, as well as being symbols of a past, less unified Europe. A lack of trust and generally negative attitudes towards the citizens of neighbouring countries also pose a challenge. A lack of trust makes people less willing to cooperate, which leads to lost opportunities to maximise the benefits that could flow from the Interreg cross-border cooperation programmes.