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.
It celebrates the success of Roman Catholic missions to promote the faith, encourages the fostering of native clergy in the countries to which the missions extended and emphasises the importance of lay Catholics as representatives of the church in non-Catholic countries.