Heinrich Denzinger, Peter Hünermann, Robert Fastiggi, et al.: Compendium of Creeds, Definitions, and Declarations on Matters of Faith and Morals (Enchiridion symbolorum…)

The standard reference for Catholic dogmatic theology. Reveals the historical development of Church doctrine through chronological arrangement of key passages from  principal magisterial source documents. Image links to free 1954 edition, which employs the pre -1963 marginal numbering system. ISBN recommendation: 0898707463

Papal Encyclicals

Papal letters to the Universal Church or, in many cases, especially before Vatican II, to the Bishops in communion with the Holy See. Worthy of special attention besides Rerum Novarum (see previous post) are Quadragesimo Anno, Mater et Magistra, Pacem in Terris, Populorum Progressio, Laborum Exercens, Sollicitudo Rei Socialis, Centesimus Annus, Caritas in Veritate, Fides et Ratio, and Spe Salvi. As of this post, the Vatican has online the encyclicals of Leo XIII, Pius X, Benedict XV, Pius XI, Pius XII, John XXIII, Paul VI, John Paul IIBenedict XVI, and Francis. ISBN recommendation: 0-87650-259-1