Vincenzo Gioacchino Raffaele Luigi Pecci was born March 2, 1810, and became Pope Leo XIII on February 20, 1878. His reign was one of the longest in history, during which he produced a total of eighty-six encyclicals-a record approached by no other pope before or since. Out of this immense canon, fifteen have been collected for this volume based on their social impact and doctrinal profundity. They cover subjects such as the proper relationship between church and state, the foundations of political authority, the study of Sacred Scripture, Christian philosophy, and Catholic Social Teaching, including Pope Leo's most famous social encyclical, Rerum Novarum. While all papal letters are timely in their own manner, these were chosen because they are, in the opinion of the publisher, most indispensable: -- Inscrutabili Dei Consilio, Aeterni Patris, Arcanum Divinae Sapientia, Diuturnum, Humanum Genus, Immortale Dei, Libertas, Exeunte Iam Anno, Sapientiae Christianae, Rerum Novarum, Providentissimus Deus, Satis Cognitum, Divinum Illud Munus, Testem Benevolentiae Nostrae, Graves de Communi Re, Mirae Caritatis.