Santiago Masarnau y Fernández (also known as Santiago Fernández de Masarnau or Santiago [de] Masarnau) (9 December 1805 in Madrid – 14 December 1882 in Madrid) was a Spanish pianist, composer and religious activist for the poor. He established the Society of Saint Vincent de Paul, an organization composed of laymen dedicated to serving the poor, in Spain. A cause for his canonization has been opened by that society.