It is a well-known scientific fact, but one that is sometimes ignored, that radio waves do not respect borders between countries and geographic regions. This means that radio networks deployed in one country or region can cause interference to networks deployed across the border. The impact of the interference can vary considerably and in the worst case may lead to network deployments and services being limited, of poorer quality, or even unavailable in localised areas. Cross border interference is of particular concern where there are long borders between adjoining countries, where there are large towns and cities close to border or where there are small countries with one or more neighbouring countries; in these cases, differences in spectrum use can limit planned spectrum awards, introduction of new technologies and network deployments. This Insight paper examines some specific examples of cross border issues and considers mitigation mechanisms available to reduce the likely impact of interference due to planned changes in the use of the radio spectrum.