The pioneer of radio communication, Guglielmo Marconi (1874-1937), had an Irish mother, Annie Jameson, and married, as his first wife, Beatrice OBrien, daughter of Lord Inchiquin of Dromoland Castle, County Clare. This study traces Marconis Irish and Italian family connections, and his work in Ireland, in particular the installations of his radio signalling stations at Crookhaven, Ballybunion and Clifden, which in 1907 was the most advanced station of its kind in the world.