Launched in January 2013, the Eusko (complementary local currency of the Northern Basque Country in France) became the first local currency in Europe five years later, with the equivalent of more than one million euros in circulation, surpassing the Chiemgauer in Germany and the Bristol Pound in England. This paper aims to explain the development of this complementary local currency and to formulate hypotheses about the factors for its success. Part 1 gives a statistical overview of the Eusko’s trajectory, analysing the distribution of this currency in its chronological and spatial dimensions. Part 2 focuses on the specificity of the territorial context, which is characterized by a high density of the associative and cooperative movements. Part 3 details the mobilizing organizational devices that contribute to the Eusko’s success.