| Main municipalities | Countries | Total population |
| Greater Copenhagen | Denmark, Sweden | 3,964,522 |
| Baarle-Hertog - Baarle-Nassau | Belgium, Netherlands | 9,262 |
| Basel - Huningue - Weil am Rhein | Switzerland, France, Germany | 2,400,000 |
| Bourg-Madame - Puigcerdà | France, Spain | |
| Como - Chiasso | Italy, Switzerland | |
| Saarbrücken - Forbach | France, Germany | 700,000 |
| Geneva - Annemasse - Ferney-Voltaire - Nyon | Switzerland, France | 890,000 |
| Gorizia - Nova Gorica | Italy, Slovenia | |
| Görlitz - Zgorzelec | Germany, Poland | 85,000 |
| Guben - Gubin | Germany, Poland | 35,000 |
| Hendaye - Irun | France, Spain | |
| Ivangorod - Narva | Russia, Estonia | 69,000 |
| Katowice - Ostrava | Poland, Czech Republic | 5,300,000 |
| Komárno - Komárom | Slovakia, Hungary | 56,000 |
| Le Perthus - Els Límits | France, Spain | 700 |
| Lille - Roubaix - Tourcoing - Mouscron - Tournai - Kortrijk | France, Belgium | 1,850,000 |
| Longwy - Aubange - Pétange | France, Belgium, Luxembourg | 80,000 |
| Strasbourg - Kehl | France, Germany | 700,000 |
| Konstanz - Kreuzlingen | Germany, Switzerland | 110,000 |
| Kerkrade - Herzogenrath | Netherlands, Germany | 95,000 |
| Frankfurt - Słubice | Germany, Poland | 75,000 |
| Haparanda - Tornio | Sweden, Finland | 32,000 |
| Pello - Pello | Sweden, Finland | 4,500 |
| Karesuando - Karesuvanto | Sweden, Finland | 500 |
| Imatra - Svetogorsk | Finland, Russia | 45,000 |
| Rousse - Giurgiu | Bulgaria, Romania | 250,000 |
| Lifford - Strabane | Ireland, United Kingdom | 18,500 |
| Valka - Valga | Latvia, Estonia | 20,000 |
| Slavonski Brod - Brod | Croatia, Bosnia and Herzegovina | 110,000 |
| Szczecin | Poland, Germany | 763,321 |
