The fiftieth anniversary of Pope Paul VI’s encyclical Populorum Progressio – it appeared at the end of March 1967 – has come and gone without receiving the attention it deserved. It was overshadowed by Humanae Vitae, which appeared 15 months later, and by the furore that surrounded the reiteration of the papal ban on artificial birth control. Yet Populorum Progressio marked a major development of church doctrine. Its significance as a milestone was recognised by Pope St John Paul II, who published Sollicitudo Rei Socialis to mark its twentieth anniversary, and by Pope Benedict XVI, whose Caritas in Veritate was a delayed tribute after its fortieth anniversary. In it, Pope Benedict described Paul VI’s encyclical as the most important Catholic social document since Rerum Novarum in 1891.