What's an Encyclical? From workers’ rights to AI, five letters from Popes that left a global impact

Pope Leo XIV on Monday presented his vision for preserving human dignity in the age of artificial intelligence by issuing his first encyclical, “Magnifica Humanitas,” or “Magnificent Humanity.”The document, presented at the Vatican alongside Christopher Olah, a founder of Anthropic, highlights how the Catholic Church continues to use one of its oldest forms of communication to address modern social and moral challenges.An encyclical is a formal letter written by a pope, usually addressed to bishops around the world. These documents are used to offer authoritative teachings on important moral, social or political issues. While they do not carry the legal status of a papal bull, Catholics are encouraged to use them as guidance in their daily lives.Though popes have written letters to the faithful since the early days of the church, Pope Benedict XIV, who led the church from 1740 to 1758, is credited with shaping the encyclical into the form recognised today.“According to its etymology, an encyclical (from the Greek egkyklios, kyklos meaning a circle) is nothing more than a circular letter. In modern times, usage has confined the term almost exclusively to certain papal documents which differ in their technical form from the ordinary style of either Bulls or Briefs, and which in their superscription are explicitly addressed to the patriarchs, primates, archbishops, and bishops of the Universal Church in communion with the Apostolic See. By exception, encyclicals are also sometimes addressed to the archbishops and bishops of a particular country,” according to the Catholic Encyclopedia.Leo XIV’s “Magnifica Humanitas” now joins a long line of influential encyclicals that shaped debate both within and beyond the Catholic Church.

Five Encyclicals that mattered

1. “Rerum Novarum” (1891) — On workers’ rightsIssued by Pope Leo XIII during the Industrial Revolution, “Rerum Novarum,” meaning “Of New Things,” became a foundation of modern Catholic social teaching.The document defended workers’ rights, including the right to form unions and earn a living wage, while rejecting both socialism and laissez-faire capitalism. It also inspired a broader social justice movement within the church, according to New York Times.It is also the encyclical that inspired the current pope’s choice of the name Leo XIV. The pope formally signed “Magnifica Humanitas” on May 15, 2026, the anniversary of “Rerum Novarum,” even though it was presented publicly 10 days later.2. “Pacem in Terris” (1963) — On world peaceWritten by Pope John XXIII during the Cold War, “Pacem in Terris,” or “Peace on Earth,” was addressed not only to Catholics but to all humanity.The encyclical called for a ban on nuclear weapons and proposed the idea of a global public authority working for the “universal common good,” with the United Nations seen as a first step.It also urged people to participate in public life “and to work together for the benefit of the whole human race.”When it was issued, The New York Times published the entire text.3. “Humanae Vitae” (1968) — On birth controlPope Paul VI’s “Humanae Vitae,” meaning “Of Human Life,” reaffirmed the Catholic Church’s opposition to artificial birth control.The central teaching of the document stated that every act of sexual intercourse must remain free from deliberate attempts to prevent conception.The encyclical immediately sparked debate among Catholics, a discussion that has continued for decades. According to a 2024 Pew Research Center poll, most Catholics in the United States and Latin America believe the church should allow artificial birth control.To help stop the spread of AIDS, many bishops later offered qualified support for teaching about condoms.4. “Caritas in Veritate” (2009) — On economicsIn “Caritas in Veritate,” or “Charity in Truth,” Pope Benedict XVI called for a major rethinking of the global economy following growing economic inequality.The encyclical criticized the widening gap between rich and poor, urged ethical behavior in finance and called on businesses to take greater social responsibility.Like “Pacem in Terris,” it also argued for a global political authority to help regulate the economy, according to NYT.Many scholars praised the document for its reflections on love, truth and justice, though critics described it as difficult to read because of its dense language and broad themes.5. “Laudato Si’” (2015) — On the environmentPope Francis’ “Laudato Si’,” meaning “Praise Be to You,” was the first encyclical entirely focused on the environment.The document framed caring for the planet as a moral and spiritual duty, rather than simply a matter of politics, science or economics. Francis also highlighted the links between climate change, poverty and social instability.The encyclical became influential in the global environmental movement, though Francis later lamented in a 2023 document that little progress had been made on ecological issues.With “Magnifica Humanitas,” Leo XIV has now placed artificial intelligence alongside workers’ rights, peace, economics, birth control and climate change as issues addressed through papal encyclicals, continuing a tradition that has shaped Catholic teaching for centuries.