(Fixes name of third encyclical)
VATICAN CITY, Feb 28 (Reuters) - Pope Benedict wrote three encyclicals on spiritual, social and economic issues during his papacy and was working on a fourth when he decided to become the first pope in some six centuries to step down instead of reigning for life.
Encyclicals are the highest form of papal writing and give the clearest indication to the world's 1.2 billion Catholics - and to non-Catholics - of what the pope and the Vatican think about specific social and moral issues.
Here is a list of the encyclicals and brief summaries of their topics.
"Deus Caritas Est" (God is Love, 2006)
In the first encyclical of his papacy, Benedict tried to guide Catholics on what they should do in a world where religion was often linked with calls for hatred and violence.
The work ranged in themes from erotic and spiritual love in a personal relationship, to the role of the Catholic Church's vast network of charity organisations around the world.
In one part of the encyclical, the pope said there was nothing wrong with erotic love between a man and a woman but that it risked reducing sex to a "commodity" it was not part of a higher spiritual love within marriage.
"In a world where the name of God is sometimes associated with vengeance or even a duty of hatred and violence, this message (of love and charity) is both timely and significant," the Pope said, explaining why he chose the theme.
"Today, the term 'love' has become one of the most frequently used and misused of words, a word to which we attach quite different meanings," he wrote.
Much of the first half is dedicated to the relationship between "eros", or erotic love, and "agape" (pronounced ah-gah-pay), the Greek word referring to unconditional, spiritual and selfless love as described in Scriptures.
The pope acknowledges that in the past the "Church, with all her commandments and prohibitions" was seen as having been "opposed to the body".
But he warns that contemporary society's way of exalting the body at all costs is deceptive and dangerous. "Eros, reduced to pure 'sex', has become a commodity, a mere 'thing' to be bought and sold, or rather, man himself becomes a commodity," he said.
"Spe Salvi" (In hope we were saved, 2007)
Benedict said atheism was responsible for some of the "greatest forms of cruelty and violations of justice" in history.
In an appeal to a pessimistic world to find strength in Christian hope, Benedict urged Christians to put their hope for the future in God and not in technology, wealth or political ideologies.
History has proven wrong ideologies such as Marxism which say humans had to establish social justice because God did not exist, the pope wrote.
"It is no accident that this idea has led to the greatest forms of cruelty and violations of justice," the pope said. Such a concept was grounded in "intrinsic falsity".
Marxism, the pope wrote, had left behind "a trail of appalling destruction" because it failed to realise that man could not be "merely the product of economic conditions".
"Caritas in Veritate" (Love in Truth, 2009)
Benedict called for a "world political authority" to manage the global economy and for more government regulation of national economies to pull the world out of the current crisis and avoid a repeat.
The encyclical called for a re-think of the way the world economy was run. It touched on a number of social issues but its main connecting thread was how the economic crisis has affected both rich and poor nations.
Parts of the encyclical upset free marketers because of its underlying rejection of unbridled capitalism and unregulated market forces, which he said had led to "thoroughly destructive" abuse of the system and "grave deviations and failures".
The pope said every economic decision had a moral consequence and called for "forms of redistribution" of wealth overseen by governments to help those most affected by crises.
In late 2012, the Vatican announced that the pope was working on a new encyclical on the subject of faith and that he would conclude it in the first half of 2013.
It would have concluded a trilogy on the three theological virtues follow the earlier ones on hope and charity. (Reporting by Philip Pullella; Editing by Alison Williams)