Geertgen tot Sint Jans, also known as Geertgen van Haarlem, Gerrit van Haarlem, Gerrit Gerritsz, Gheertgen, Geerrit, Gheerrit, or any other diminutive form of Gerald, was an Early Netherlandish painter from the northern Low Countries in the Holy Roman Empire. No contemporary documentation of his life has been traced, and the earliest published account of his life and work is from 1604, in Karel van Mander's Schilder-boeck.
According to van Mander, Geertgen was probably a pupil of Albert van Ouwater, one of the first oil painters in the northern Low Countries. Both painters lived in the city of Haarlem, where Geertgen was attached to the house of the Knights of Saint John, perhaps as a lay brother, for whom he painted an altarpiece. In van Mander's book he states that Geertgen took the name of St. John without joining the order, thus his last name "tot Sint Jans" was derived from the order's name and means "unto Saint John".