The Hagia Sophia is a church located in Thessaloniki, Greece. With its current structure dating from the 7th century, it is one of the oldest churches in the city still standing today. Because of its outstanding Byzantine art and architecture, in addition to its importance in early Christianity, it is one of several monuments in Thessaloniki listed as a UNESCO World Heritage Site in 1988.

The city of Thessaloniki in Macedonia, Greece, for several centuries the second-most important city of the Byzantine Empire, played an important role for Christianity during the Middle Ages and was decorated by impressive buildings. Because of Thessaloniki's importance during the early Christian and Byzantine periods, the city contains several Paleochristian monuments that have significantly contributed to the development of Byzantine art and architecture throughout the Byzantine Empire and Serbia. The evolution of Imperial Byzantine architecture and the prosperity of Thessaloniki go hand in hand, especially during the first years of the Empire, when the city continued to flourish. Despite the capture of Thessaloniki by the Ottoman Empire in 1430, the Christian monuments were not destroyed, and travelers such as Paul Lucas and Abdulmejid I document the city's wealth in Christian monuments during the Ottoman control of the city.