The new territorial structures for the governance of the borderlands between Portugal and Spain (Eurocities) constitute a novel and exciting example of a local commitment to cross-border cooperation (CBC). The Eurocities are feasible institutions in very close cities and municipalities, and have always had intense relationships. With different speeds, formats and intensities, Eurocities have been forming along the European Union’s internal borders. Compared to other types of cooperation entities created mainly at regional or sub-regional scales (Euroregions and Eurodistricts), Eurocities are created at the municipal or local level, which are the most relevant protagonists of cross-border flows and relations. These new institutions are established based on different common objectives, such as economic dynamism, tourism, mobility, sustainability and access to funding, among many other fields of common interest. The present research deals with the geographical and institutional framework of these new Eurocities on the Portuguese–Spanish border, where they have increased in recent years. Their beginnings, evolution and characteristics are analyzed through a review work. In many cases, Eurocities become responses at the local and municipal scales. Some of these Eurocities have gone one step further by becoming a European Grouping of Territorial Cooperation (EGTC), such as Chaves–Marín or Guadiana Eurocity. In addition, some of these second-generation CBC structures are integrating into higher regional levels, such as in the case of the Río Minho EGTC. Furthermore, the present study enables us to identify factors, such as the offer of common equipment and services offer, Eurocitizenship, enhancing access to European Funds, or the marketing and advertising of the Eurocity, as some of the critical factors for the success of the Iberian Eurocities.