Pope Pius X - Papacy extended from 1903-1914.
Church teachings regarding Catholic Social Justice are culled from scripture, the Catechism, encyclicals and other church magisterium documents. While many Church documents touch on the "Social" mission of the Church, there is no definitive list of "Catholic Social Teaching" documents. The list of resources below represents some of the major resources that are often cited when authors and experts talk about "Catholic Social Justice" and Catholic Social Teaching. Links below are hosted on the Vatican website, where you may also find translations in various languages.
The Encyclicals below are often written in response to what is going on "at the time." The Church offers advice on how to best live up to Catholic Principles in the current day, and analyzes any movements according to whether they endanger the dignity of the human person.
The Compendium of the Social Doctrine of the Church is the most thoroughgoing compilation of primary Biblical and Magisterial resources arranged by themes and thoughts on Catholic Social Thought. Other collections of Catholic Social teaching in "Thematic form" can be found on the Social Agenda website (also in several languages). The Office of Social Justice in Minnesota offers the original documents with "concordances" and "notable quotations."
Rerum Novarum -- Leo XIII (1891)
Quadragesimo Anno (After Forty Years) -- Pius XI (1931)
Mater et Magistra (Christianity and Social Progress) -- John XXIII (1961)
Pacem in Terris -- John XXIII (1963)
Populorum Progressio -- Paul VI (1967)
Octogesima Adveniens (A Call to Action) -- Paul VI (1971)
Laborem Exercens (On Human Work) -- John Paul II (1981)
Sollicitudo rei Socialis -- John Paul II (1987)
Centesimus Annus -- John Paul II (1991)
Evangelium Vitae -- John Paul II (1995)
Deus Caritas Est -- Benedict XVI (2005)