Niccolò di ser Sozzo was a prolific 14th century Italian painter and illuminator of the Sienese school. Where Niccolò’s altarpieces followed the conventional styles of the time, his illuminations were often more inventive and original. Among the manuscripts to which he contributed are Beinecke 1112, a Cistercian breviary made for the monks of San Galgano, and a page included in the Caleffo dell’Assunta, a register of Sienese public documents transcribed in 1334-6. This latter is his only signed work, and depicts the Assumption of the Virgin. From the sources containing his miniatures, we can infer that Niccolò worked for a wide range of patrons, both lay and religious, and for different houses, both Cistercian and, as in the case of Barnard 1, Franciscan.