Social Encyclicals, according to the Social Encyclicals entry in Encyclopedia of Catholic Social Thought, Social Science, and Social Policy are: "A large-scale, detailed letter sent out by the pope to everyone in the world, treating social issues (usually economic ones) with a combination of critique and counsel, defining paramount principles, pointing out urgent problems suggesting a direction for solutions." (Edited by Michael Coulter [et al.], Scarecrow Press, Inc. 2007, page 978)

The major social encyclicals in chronological order:

Rerum Novarum: On the Condition of Workers

Promulgated by Leo XIII in 1891 this encyclical is a response to the effects of industrialization on persons and communities.  According to the Rerum Novarum entry in the New Catholic Encyclopedia, the encyclical is comprised of five parts: examination of the working class, the role of the church in social affairs, alleviating poverty, rejection of laissez-faire and promotion of volunteer organizations. (Edited by Bernard L. Marthaler [et al.], The Catholic University of America Press, 2003, volume 12, page 136)

Quadragesimo Anno: On the Reconstruction of the Social Order

Pope Pius XI promulgated Quadragesimo Anno in 1931, during the great depression.  This letter critiqued the current economic system and sought to promote institutional reform.  The encyclical reviews catholic social teaching and calls for catholic social action. (New Catholic Encyclopedia, Edited by Bernard L. Marthaler [et al.], The Catholic University of America Press, 2003, volume 11, page 847) 

Mater et Magistra: Mother and Teacher

Promulgated by John XXIII in 1961, this letter deals with Christian teaching on modern social questions.  It's entry in New Catholic Encyclopedia states that it has four sections that address the following issues: clarification of previous papal statements on catholic social thought, analysis of Leo's major areas of teaching, problems of agricultural economies, and the importance of truth, justice and love in rebuilding a sound social order. (Edited by Bernard L. Marthaler [et al.], The Catholic University of America Press, 2003, volume 9, page 317)

Pacem in Terris: Peace on Earth

Promulgated by John XXIII in 1963 this encyclical states that respect for the law of God dictates unity with the range of order in human affairs.  According to its entry in New Catholic Encyclopedia, the four parts of this encyclical deal with individual responsibility, relationship between people and the laws that govern them, government responsibility, and a call for governments to be interdependent on each other.  (Edited by Bernard L. Marthaler [et al.], The Catholic University of America Press, 2003, volume 10, page 741)

Octogesima Adveniens:  A Call to Action  (This is an Apostolic Letter)

This apostolic letter was promulgated by Pope Paul VI.  "On May 15, 1971, commemorating the 80th anniversary of Pope Leo XIII's encyclical Rerum novarum on the reform of the social order, Pope Paul issued a forceful apostolic letter, Octogesima adveniens with particular insistence on the necessity of involvement of all men in the solution of the problems of justice and peace."(Paul VI. 2009, from Encyclopædia Britannica Online: http://search.eb.com/eb/article-5551) 

Populorum Progressio: On the Development of People

Promulgated by Pope Paul VI in 1967, this letter supports the plight of those who are striving to escape poverty or misery.  New Catholic Encyclopedia explains that the three parts of the letter deal with human development and the drive to see more, know more and do more, human solidarity and a plea to accept responsibility for the whole of humanity. (Edited by Bernard L. Marthaler [et al.], The Catholic University of America Press, 2003, volume 11, pages 516-517)

Laborem Exercens: On Human Work

This encyclical was promulgated by Pope John Paul II in 1981.  The Laborem Exercens entry in New Catholic Encyclopedia states that, "The encyclical presented Catholic social teaching as a radical critique of communism and capitalism.  Oppression and inequality in the world are caused by a disorder and in the organization of labor." (Edited by Bernard L. Marthaler [et al.], The Catholic University of America Press, 2003, volume 8, page 266)

Sollicitudo Rei Socialis: On the Twentieth Anniversary of Populorum Progressio

Promulgated by Pope John Paul II in 1987, New Catholic Encyclopedia says of this letter, "John Paul II presents a series of reflections on the requirements of authentic human development, the international duty of solidarity, and the social responsibility of the church." (Edited by Bernard L. Marthaler [et al.], The Catholic University of America Press, 2003, volume 8, page 266)

Centesimus Annus:  The Hundredth Anniversary of Rerum Novarum

Promulgated by Pope John Paul II in 1991, this encyclical marks the 100 year anniversary of the original Social Encyclical, Rarum Novarum.  Six sections address dignity and rights of workers, history of the communist threat since the original document, analysis of the fall of communism, purpose of material goods, human freedom and it's relation to ultimate truth, and the church's social doctrine as inspired by care for each human being. (New Catholic Encyclopedia, Edited by Bernard L. Marthaler [et al.], The Catholic University of America Press, 2003, volume 3, page 343)

Caritas in Veritate

Pope Benedict XVI promulgated this encyclical in 2009.  According to John Carr of the United States Conference of Catholic Bishops,  "In his new encyclical Caritas in Veritate (Charity in Truth), Pope Benedict XVI offers an ethical analysis of the global economic crisis and an essential moral framework on how to move forward as one human family."  (http://www.usccb.org/jphd/caritasinveritate/index.shtml)