Theodor Hagen [often spelled Theodore Hagen] (15 April 1823, Hamburg – 27 December 1871, New York City) was a writer on musical topics in Germany and the United States.
He was a member of the local Communist League in Hamburg, Germany and took part in the publication and distribution of the Neue Rheinische Zeitung Politisch-ökonomische Revue.
Soon after his return to Germany he became known as a writer on musical topics, especially as a contributor to Robert Schumann's Neue Zeitschrift für Musik.
He came to New York in 1854, and assumed the editorship of The Musical Gazette which was at the end of about six months consolidated with another journal under the title of The Musical Review and Gazette.
This United States musical biography article is a stub.