Since it looks like Pope Benedict's long-awaited social encyclical, Caritas in Veritate, will be appearing any day now (he reportedly signed it Monday), it's probably a good time to take a look at the history of Catholic social teaching, specifically as it has been expressed through papal encyclicals.
Here are the highlights:
Rerum Novarum (Of New Things) 1891, Pope Leo XIII -- essentially the Big Bang of Catholic social teaching, truly groundbreaking, and the standard that popes have looked back to ever since (see below). This encyclical tackles the turmoil surrounding labororers in the wake of the Industrial Revolution, touching on issues including socialism, unbridled capitalism, a living wage, the relationship between laborer and employer, and the relationship between classes. Pope Leo also makes a first mention of the preferential option for the poor.
Quadragesimo Anno (After Forty Years) 1931, Pope Pius XI -- following Rerum Novarum by exactly 40 years, this encyclical offers an update on the state of labor and industrialization, also offering strong critiques of communism, unrestrained capitalism and classism.
Mater et Magistra (Mother and Teacher) 1961, Pope John XXIII -- issued 70 years after Rerum Novarum, this encyclical looks to the Church as the "Mother and Teacher," calling the world to salvation and better social relationships with one another. It looks at science and technology, noting both their power to improve the human condition, but also to limit human freedoms, calling on governments to safeguard against this and ensure human rights. The encyclical calls on wealthier nations to help poorer ones. It also criticizes ideologies (not specifically naming communism) that promise to create a paradise in this world, while disregarding religion.
Pacem in Terris (Peace on Earth) 1963, Pope John XXIII -- issued only two months before the pope's death, this encyclical is the first ever to be directed to "all men of good will," instead of just the world's Catholics. In a response to the Cold War, the encyclical outlines necessary conditions for a lasting world peace, looking at the rights of individuals, the relationships between individuals and states, the relationships between states, and the relationship between leaders and the whole world.
Populorum Progressio (On the Development of Peoples) 1967, Pope Paul VI -- this encyclical, which Benedict's new encyclical is believed to echo, looks at the economy on a global level and addresses the rights of workers to unionize and to have secure employment, decent working conditions.
Laborem Exercens (On Human Work) 1981, Pope John Paul II -- issued in honor of the 90th anniversary of Rerum Novarum, this encyclical once again looks at the rights and dignity of workers, with emphases including disabled workers, emigration, materialism, and the spirituality of work.
Sollicitudo Rei Socialis (On Social Concern) 1987, Pope John Paul II -- this encyclical honored Populorum Progressio on its 20th anniversary, offering a then-contemporary reading of the challenges first addressed in the earlier encyclical.
Centesimus Annus (The Hundredth Year) 1991, Pope John Paul II -- on the 100th anniversary of Rerum Novarum, John Paul II reflected on the current state of issues that Leo XIII had assessed in his day. Leo XIII had issued warnings about socialism before it had developed into a movement. John Paul II wrote in the immediate wake of the fall of communism.
Evangelium Vitae (The Gospel of Life) 1995, Pope John Paul II -- an affirmation of the gift of human life and the need to protect it, this encyclical dealt with widespread abortion, the threat of euthanasia and renewed use of the death penalty.
Deus Caritas Est (God is Love) 2005, Pope Benedict XVI -- Benedict's first encyclical, that could have been an abstract or scholarly treatise, instead dug deep into the concept of love and cited the connections between love of God and love of neighbor. Pope Benedict said the Church could no more neglect charity than it could Scripture or the sacraments and even called charity a manifestation of Trinitarian love.
Caritas In Veritate (Charity in Truth) 2009, Pope Benedict XVI -- anticipated since 2007, this encyclical is believed to follow up on the themes of Populorum Progressio. Dealing with the ethics of contemporary economics, it's reasonable to think that the global economic crisis will weigh in heavily on what the pope has to say.