Acta Apostolicae Sedis (Latin for "Acts of the Apostolic See"), often cited as AAS, is the official gazette of the Holy See, appearing about twelve times a year. It was established by Pope Pius X with the decree Promulgandi Pontificias Constitutiones (29 September 1908), and publication began in January 1909. It contains all the principal decrees, encyclical letters, decisions of Roman congregations, and notices of ecclesiastical appointments. The laws contained in it are to be considered promulgated when published, and effective three months from date of issue, unless a shorter or longer time is specified in the law.
It replaced a similar publication that had existed since 1865, under the title of Acta Sanctae Sedis. Though not designated as the official means of promulgating laws of the Holy See, this was on 23 May 1904 declared an organ of the Holy See to the extent that all documents printed in it were considered "authentic and official". As indicated above, the Acta Sanctae Sedis ceased publication four years later.
Acta Apostolicae Sedis is published in Latin.
Since 1929, Acta Apostolicae Sedis carries a supplement in Italian, called Supplemento per le leggi e disposizioni dello Stato della Città del Vaticano, containing laws and regulations of Vatican City, the city-state founded in that year. In accordance with paragraph 2 of the Legge sulle fonti del diritto of 7 June 1929, the laws of the state are promulgated by being included in this supplement.