John Frederick Haldon FBA (born 23 October 1948 in Newcastle upon Tyne) is a British historian, and Shelby Cullom Davis '30 Professor of European History emeritus, professor of Byzantine history and Hellenic Studies emeritus, as well as former director of the Mossavar-Rahmani Center for Iran and Persian Gulf Studies at Princeton University.
 Haldon received his bachelor's degree from the University of Birmingham in 1970, with a thesis on "Arms, armour and tactical organisation of the Byzantine army from Maurice to Basil II", and his master's degree from the Ludwig Maximilian University of Munich in Germany. He returned to the University of Birmingham to complete his PhD in 1975 on "Aspects of Byzantine military administration: the Elite Corps, the Opsikion, and the Imperial Tagmata from the sixth to the ninth century" under the supervision of Anthony Bryer. Haldon also studied Modern Greek at the University of Athens. He initially wanted to study Roman-British history and work on post-Roman Britain, but eventually changed his field of study.
 After graduating from the University of Birmingham, Haldon held a post-doctoral fellowship at the Institut für Byzantinistik of the Ludwig Maximilian University of Munich (1976–1979). From 1980 to 1995, he was junior professor at the University of Birmingham. From 1995 to 2000, he was director of the Centre for Byzantine, Ottoman and Modern Greek Studies at the University of Birmingham. From 2000 to 2005, Haldon served as head of the School of Historical Studies at the University of Birmingham. 
 In 2005 he joined the faculty of Princeton University, where he was professor of Byzantine history and Hellenic studies and (from 2009) the Shelby Cullom Davis Professor of European History until his retirement in 2018. He was concurrently a senior fellow at the Dumbarton Oaks Center for Byzantine Studies in Washington, D.C. from 2007 to 2013. At Princeton, Haldon also served as the director of graduate studies for the History Department (2009–2018) and as the founding director of the Mossavar-Rahmani Center for Iran and Persian Gulf Studies (2013–2018). He was the overall director of the Avkat Archaeological Project (2006–2012, fieldwork completed by 2010) under the aegis of the British Institute at Ankara. From 2013 he has been director of the Princeton Climate Change and History Research Initiative, and since 2018 director of the Environmental History Lab for the Program in Medieval Studies. 
 He is the author and co-author of nearly 20 books, including six monographs: The Empire That Would Not Die: The Paradox of Eastern Roman Survival, 640–740 (2016), Byzantium in the Iconoclast Era c. 680–850: A History (with Leslie Brubaker, 2011), Warfare, State and Society in the Byzantine World, 565–1204 (1999), The State and the Tributary Mode of Production (1993), Byzantium in the Seventh Century: The Transformation of a Culture (1990) and Byzantine Praetorians: An Administrative, Institutional and Social Survey of the Opsikion and Tagmata, c. 580–900 (1984).
 His research focuses on the history of the medieval eastern Roman (Byzantine) empire, in particular in the period from the seventh to the twelfth centuries; on state systems and structures across the European and Islamic worlds from late ancient to early modern times; on the impact of environmental stress on societal resilience in premodern social systems; and on the production, distribution and consumption of resources in the late ancient and medieval world.