Princeps Pastorum (Latin for 'Prince of the shepherds') is the title of an encyclical letter promulgated by Pope John XXIII on November 28, 1959. It is derived from a biblical passage: I Peter 5:4. In its English translation the letter opens with the phrase On the day when "the Prince of the Shepherds" entrusted to Us His lambs and sheep. It refers to Jesus Christ.