Boleslaw the Pious (1224/27 – April 14, 1279) is a Duke of Greater Poland during 1239–1247 (according to some historians during 1239–1241 sole Duke of Ujście), Duke of Kalisz during 1247–1249, Duke of Gniezno during 1249–1250, Duke of Gniezno-Kalisz during 1253–1257, Duke of whole Greater Poland and Poznań during 1257–1273, in 1261 ruler over Lad, regent of the Duchies of Masovia, Plock and Czersk during 1262–1264, ruler over Bydgoszcz during 1268–1273, Duke of Inowrocław during 1271–1273, and Duke of Gniezno-Kalisz since 1273 until his death.

He is the second son of Władysław Odonic, Duke of Greater Poland by his wife Hedwig, who was probably daughter of Duke Mestwin I of Pomerania, or a member of the Premyslid dynasty.

His name is very popular in the Piast dynasty, so it's unknown exactly after whom he was named.

Very soon Bolesław received the nickname of "the Pious" (Latin: Pius), given to him during his lifetime by the Chronicle of the Chapter of Poznań.