This is the first ever biography of (Edward) Swan Hennessy (1866–1929), an Irish-American composer who came to live in Paris from around 1903. Born in Rockford, Illinois, he grew up in Chicago, studied at the conservatory of music in Stuttgart, Germany, lived in various places across Europe, finally settling in the most vibrant musical metropolis of the time. Here he became influenced by the French Impressionists and tried to adapt his work to his musical environment as best as he could – or, perhaps, insofar as this was allowable. From 1912 – and especially after World War I – he realised his true mission: as a member of a group of Celticist Breton composers, he built upon his Irish heritage and henceforth wrote in a uniquely ‘Celtic’ style, fusing characteristics of Irish traditional music with the art music of his time.