A Papal brief is a formal document emanating from the Pope, in a somewhat simpler and more modern form than a Papal bull.
The introduction of briefs, which occurred at the beginning of the pontificate of Pope Eugenius IV (3 March 1431 – 23 February 1447), was prompted for the same desire for greater simplicity and expedition that had already been responsible for the disappearance of the greater bulls and the general adoption of the less cumbersome mandamenta. A brief (from the Latin "breve" for "short") was a compendious Papal letter which dispensed with some previous formalities.
A brief was written on vellum, generally closed, i. e., folded, and sealed in red wax with the Papal ring of the fisherman. The Pope's name appears first and at the top, normally written in capital letters, e. g.: "PIUS PP III", and instead of the formal salutation in the third person used in Papal bulls, the brief at once adopts a direct form of address, e. g., "Dilecte fili—Carissime in Christo fili", the phrase being adapted to the dignity and character of the addressee. The letter begins by way of preamble with a statement of the case and cause of writing and is followed by certain instructions without minatory clauses or other formulae. At the end the date is expressed by the day of the month and year with a mention of the seal, for example in this form: "Datum Romae apud Sanctum Petrum, sub annulo Piscatoris die V Marii, MDLXXXXI, pont. nostri anno primo". The year here specified, which is used in dating briefs, is probably to be understood in any specific instance as the year of the Nativity, beginning 25 December. However, this is not an absolute rule, and the sweeping statements sometimes made in this matter are not to be trusted, for it is certain that in some instances the years meant are ordinary calendar years, i. e., years beginning with the first of January. (See Giry, "Manuel de diplomatique," pp. 126, 696, and 700.)
A similar want of uniformity is generally observed in the dating of bulls from the middle of the eleventh century to the end of the eighteenth: Papal bulls were dated by the years of the Incarnation, commencing on 25 March, the Solemnity of the Annunciation. After the institution of briefs by Pope Eugenius IV, the use of even lesser bulls, in the form of mandamenta, became notably less frequent. Still, for many purposes, bulls continued to be employed, for example in canonizations, in which case special forms are observed, the Pope by exception signing his own name, under which is added a stamp imitating the rota as well as the signatures of several cardinals, as also in the nominations of bishops, promotions to certain benefices, some marriage dispensations, et cetera. But the choice of the precise form of instrument was often arbitrary. For example, in granting the dispensation which enabled King Henry VIII of England to marry his brother's widow, Catherine of Aragon, 2 forms of dispensation were issued by Pope Julius II, one a brief, seemingly expedited in great haste, and the other a bull which was sent on afterwards. Similarly we may notice that, while the English Catholic hierarchy was restored in 1850 by a brief, Pope Leo XIII in the first year of his reign used a bull to establish the Catholic episcopate of Scotland. So also the Society of Jesus, suppressed by a brief in 1773, was restored by a bull in 1818. A very interesting account of the formalities which had to be observed in procuring bulls in Rome at the end of the fifteenth century is contained in "Practica" by Schmitz-Kalemberg (1904).