Napoleone Colajanni (Castrogiovanni, 27 April 1847 – Castrogiovanni, 2 September 1921) was an Italian writer, journalist, criminologist, socialist and politician. In the 1880s he abandoned republicanism for socialism, and became Italy's leading theoretical writer on the issue for a time. He has been called the father of Sicilian socialism. Due to the Socialist party's discourse of Marxist class struggle, he reverted in 1894 to his original republicanism. Colajanni was an ardent critic of the Lombrosian school in criminology. In 1890 he was elected in the national Italian Chamber of Deputies and was re-elected in all subsequent parliaments until his death in September 1921.