Angeliki Laiou (Greek: Αγγελική Λαΐου; Athens, 6 April 1941 – Boston, 11 December 2008) was a Greek-American Byzantinist.
Laiou was born in Athens on 6 April 1941 to a Pontic family, refugees from the Black Sea coast of modern Turkey. She studied at the Athens College and continued her studies in the Philosophy School of the University of Athens (1958–59), where she studied under the Greek Byzantinist Dionysios Zakythinos, who awakened her interest in the Byzantine Empire. She moved to Brandeis University from where she graduated with her BA in 1961, and completed a post-graduate course and received her PhD from Harvard in 1966, under the supervision of Robert Lee Wolff, one of the leading historians of the Crusades. Her doctoral thesis became the basis for her first book, published in 1972 as Constantinople and the Latins: The Foreign Policy of Andronicus II, 1282–1328.
In 1962, she went to lecture at the University of Louisiana, before returning to Harvard, where she stayed from 1966 to 1972, first as instructor and then as assistant professor. She then moved to Brandeis, where she remained until 1981, becoming distinguished professor. During this period, she also taught at Rutgers College of Rutgers University. In 1981, she returned to Harvard to occupy the prestigious Dumbarton Oaks Professorship of Byzantine Studies, a post she held until her death. In 1985–88, she served as the head of Harvard's History Department—the first woman to head a department at Harvard—and from 1989 until 1998 she headed the distinguished Dumbarton Oaks Research Library and Collection in Washington, DC—again the first woman to do so.