The Mother of God of the Life-giving Spring or Life-giving Font (Ancient Greek: Ζωοδόχος Πηγή, romanized: Zōodóchos Pēgḗ, modern pronunciation: [zo.oˈðoxos piˈʝi]; Russian: Живоно́сный Исто́чник, romanized: Zhivonósny Istóchnik, IPA: [ʐɨvɐˈnosnɨj ɪˈstotɕnʲɪk]) is an epithet of the Holy Theotokos that originated with her revelation of a sacred spring (Ancient Greek: ἁγίασμα, romanized: hagíasma) in Valoukli, Constantinople, to a soldier named Leo Marcellus, who later became Byzantine Emperor Leo I (457-474). Leo built the historic Church of St. Mary of the Spring over this site, which witnessed numerous miraculous healings over the centuries, through her intercessions, becoming one of the most important pilgrimage sites in Greek Orthodoxy. Thus the term "Life-giving Font" became an epithet of the Holy Theotokos and she was represented as such in iconography.

The feast day of the Life-giving Spring is celebrated on Bright Friday in the Eastern Orthodox Church, and in those Eastern Catholic Churches which follow the Byzantine Rite. Additionally, the icon of the Theotokos the "Life-giving Spring" is commemorated on April 4 / 17 in Slavic Orthodox churches.

Outside the Imperial City of Constantinople, near the Golden Gate (Porta Aurea) used to be found a grove of trees. A shrine was located there with a spring of water, which from early times had been dedicated to the Theotokos. Over time, the grove had become overgrown and the spring became fetid.

The traditional account surrounding the feast of the Life-Giving Spring is recorded by Nikephoros Kallistos Xanthopoulos, the last of the Greek ecclesiastical historians, who flourished around 1320. It begins with a miracle that occurred involving a soldier named Leo Marcellus, the future Byzantine Emperor Leo I. On April 4, 450, as Leo was passing by the grove, he came across a blind man who had become lost. Leo took pity on him, led him to the pathway, seated him in the shade and began to search for water to give the thirsty man. Leo heard a voice say to him, "Do not trouble yourself, Leo, to look for water elsewhere, it is right here!" Looking about, he could see no one, and neither could he see any water. Then he heard the voice again,

"Leo, Emperor, go into the grove, take the water which you will find and give it to the thirsty man. Then take the mud [from the stream] and put it on the blind man's eyes.... And build a temple [church] here ... that all who come here will find answers to their petitions."

Leo did as he was told, and when the blind man's eyes were anointed he regained his sight.

After his accession to the throne, the Emperor erected a magnificent church on this site, dedicated to the Theotokos, and the water continued to work miraculous cures, as well as resurrections from the dead, through the intercession of the Theotokos, and therefore it was called "The Life-Giving Spring."

Historians Procopius and Cedrenus state that Emperor Justinian erected a new church, larger than the first, in the last years of his reign (559-560), utilizing materials that had remained after the erection of the Hagia Sophia. After the erection of the sanctuary, the Byzantines named the Gate that was situated outside the walls of Theodosius II "Gate of the Spring" (Ancient Greek: Πύλη τῆς Πηγῆς, romanized: Pýlē tês Pēgês).