Philostorgius was a Christian church historian who lived during the late 4th and early 5th centuries CE. He was born in Cappadocia around 368 CE into a family that belonged to the Eunomian sect, a branch of Christianity that held unorthodox views on the relationship between God the Father and the Son. He was educated in Constantinople by leading Eunomian theologians and became a committed adherent of their teachings.

His major work was a 12-volume Ecclesiastical History, covering events from roughly 300 to 425 CE. The original text is lost, but its content is known through fragments and a detailed summary made by the 9th-century patriarch Photius, who strongly disagreed with Philostorgius's theology. He also wrote at least two other treatises, which are now lost. Philostorgius traveled to gather material for his history, which included not only church affairs but also secular events, geographical details, and accounts of natural phenomena.

According to modern scholars, Philostorgius's primary significance is as the only historian to write from a Eunomian perspective. His work provides a valuable dissenting narrative to the orthodox church histories of his time. While his theological views were condemned as heretical, his history preserved unique historical and scientific information. The survival of his work through Photius allows academics to study an important alternative voice from the intense theological controversies of the early Christian church.