Alfredo Cristiano Keil (3 July 1850 – 4 October 1907) was a Portuguese romantic composer and painter.

Keil was born in Lisbon, the son of Johann Christian Keil (son of Johann Georg Keil and wife Elisabeth ...) and wife (m. Lisbon, 30 August 1848) Maria Josefina Stellflug (daughter of Matias Stellflug and wife Barbara ...). He was of German origin, and was the great Portuguese romantic composer. He was also considered the last important Portuguese painter in the Romantic style. He studied in Munich and Nuremberg with the German romantic painters Kaulbach and von Kreling. Returning to Portugal, where he continued his studies, he became a well known romantic painter, being also the contemporary of the Naturalist generation, with his melancholic intimate scenes and landscapes.

As a composer, he gained prominence with his operas Donna Bianca (1888), Irene (1893) and Serrana (1899), then considered the best Portuguese opera.

He composed the music of A Portuguesa, the Portuguese national anthem, in 1891, with lyrics by poet and playwright Henrique Lopes de Mendonça; it was officially adopted in 1911, after the proclamation of the Republic the previous year. Ironically, he died, in Hamburg, almost exactly three years before the first day of the Revolution.