The primary source of the Church's teachings on Social Justice is God's revelation through Jesus Christ. This is expressed through both Scripture, and the Tradition of the Church as the fundamental ideas and principles of Social Justice are applied to particular circumstances, issues and situations.
The most important resource for Catholics is the Social Encyclicals of the modern Popes, from Pope Leo XIII to Pope Benedict XVI, which you can find at the Vatican web site.
The briefest comprehensive statement of Catholic Social Teaching is the Seven Key Themes from the United States Conference of Catholic Bishops.
The most recent Papal Encycclical on Social Justice was publiches in 2009 by Pope Benedict XVI:
Caritas in Veritiatae (Love in Truth)
See various comments on this document from:
See also the Pontifical Council for Justice and Peace
The United States Conference of Catholic Bishops produce many social justice documents, focused on domestic issues in the USA and America's relations with other nations. See in particular:
See also the Bishops Conference collection on Life Issues:
“We … call for a civil dialogue and prudent and constructive action to protect God’s precious gift of the earth’s atmosphere with a sense of genuine solidarity and justice for all God’s children.”
—U.S. Catholic Bishops
What are the moral implications of climate change? Who is most impacted? What should the Catholic community do? The Catholic Coalition on Climate Change was launched in 2006 to help the U.S. Conference of Catholic Bishops (USCCB) and the Catholic community address these issues.
Learn about Catholic Principles and Teachings applied to the issue of global climate change:
Catholic Coalition on Climate Change supports and complements USCCB’s Office of Social Development and World Peace and the bishops' Environmental Justice Program. The Coalition is funded with generous assistance from the National Religious Partnership for the Environment.
Please read and sign the Catholic Climate Covenant