Carl Gustav Adolf Siegfried (22 January 1830, Magdeburg – 9 January 1903, Jena) was a German theologian who specialized in Old Testament studies.
He studied theology and philology at the universities of Halle and Bonn. In 1859 he received his doctorate from Halle, and afterwards worked as a teacher at the cathedral gymnasium in Magdeburg and at the regional school in Pforta. In 1875, he was appointed professor of Old Testament theology at the University of Jena.
Siegfried was the author of many articles in the Allgemeine Deutsche Biographie.