The word “encyclical” comes from the Greek, meaning “circular.” An encyclical was originally a circular letter sent to all the churches of a particular area in the ancient Roman Church. Today it refers to a formal written teaching by the Pope on a significant issue relevant to the faithful, and the life of the Church.
Comparing an encyclical to other kinds of official Roman Catholic documents is a good way to understand the significance of an encyclical. Usually when the pope makes a declaration of some article of faith or moral law it is given in the form of a Papal Bull, which is very formal and uses prescriptive and dogmatic language. These are rare in recent times. Then there are Decrees, which address a very particular problem requiring precise response and action. A third style of Papal documents are Apostolic letters and messages, which are characteristically pastoral, encouraging, and inspirational.
Encyclicals can have some features of all these categories but are generally longer; the thinking behind the statements are deeper and articulated more expansively. The title of the encyclical is always taken from the first words of the opening sentence. ‘Laudato si’, for example, is the beginning of the Pope Francis’ encyclical on ecology, and is taken from the Canticle of the Sun of St. Francis “Be praise, my Lord, through all your creatures, especially through my lord Brother Sun.”
Encyclicals are addressed usually to the whole church (a few exceptions have been addressed to bishops of particular nations) and it is understood that bishops will promulgate the teachings and make the encyclicals widely available. While the original text has been, and still is written in Latin, today encyclicals are widely translated, and available on the Vatican’s website.
Since 1854 (during the term of Pope Pius IX) there have been 240 encyclicals. However, it is noteworthy that the number of encyclicals written by more recent popes is less than the number written by earlier popes in this period. Pius XII (pope from 1939-1958) wrote 40 encyclicals and Leo XIII (1878-1903) wrote 87. John Paul II (1978-2005) wrote 14 and Benedict (2005-2013) only 3. This is because writings that might have been calles an encyclical might now be called something else, and also, through modern media popes can more easily teach to the faithful than was possible in the past.