Ernst Moritz Theodor Ziller (; Greek: Ερνέστος Τσίλλερ, Ernestos Tsiller [ˈtsiler]; 22 June 1837 – 4 November 1923) was a German-born university teacher and architect who later became a Greek national. In the late 19th and early 20th centuries, he was a major designer of royal and municipal buildings in Athens, Patras, and other Greek cities.