A proclamation (Lat. proclamare, to make public by announcement) is an official declaration.

In English law, a proclamation is a formal announcement ("Royal Proclamation"), made under the great seal, of some matter which the King in Council or Queen in Council desires to make known to his or her subjects: e.g., the declaration of war, the statement of neutrality, the summoning or dissolution of Parliament, or the bringing into operation of the provisions of some statute the enforcement of which the legislature has left to the discretion of the king in the announcement

Royal proclamations of this character, made in furtherance of the executive power of the Crown, are binding on the subject, "where they do not either contradict the old laws or tend to establish new ones, but only confine the execution of such laws as are already in being in such matter as the sovereign shall judge necessary" (Blackstone's Commentaries, ed. Stephen, ii. 528; Stephen's Commentaries, 14th ed. 1903, ii. 506, 507; Dicey, Law of the Constitution, 6th ed., 51). Royal proclamations, which, although not made in pursuance of the executive powers of the Crown, either call upon the subjects to fulfil some duty which they are by law bound to perform, or to abstain from any acts or conduct already prohibited by law, are lawful and right, and disobedience to them (while not of itself a misdemeanour) is an aggravation of the offence (see charge of Chief Justice Cockburn to the grand jury in R. v. Eyre (1867) and Case of Proclamations 1610, 12 Co. Rep. 74.

The Crown has from time to time legislated by proclamation; and the Statute of Proclamations 1539 provided that proclamations made by the king with the assent of the council should have the force of statute law if they were not prejudicial to "any person's inheritance, offices, liberties, goods, chattels or life." But this enactment was repealed by an act of 1547; and it is certain that a proclamation purporting to be made in the exercise of legislative power by which the sovereign imposes a duty to which the subject is not by law liable, or prohibits under penalties what is not an offence at law, or adds fresh penalties to any offence, is of no effect unless itself issued in virtue of statutory authority (see also order in council).

The Crown has power to legislate by proclamation for a newly conquered country (Jenkyns, British Rule and Jurisdiction beyond the Seas); and this power was freely exercised in the Transvaal Colony during the Second Boer War. In the British colonies, ordinances are frequently brought into force by proclamation; certain imperial acts do not take effect in a colony until they are proclaimed (e.g. the Foreign Enlistment Act 1870); and proclamations are constantly issued in furtherance of executive acts. In many British protectorates the high commissioner or administrator was empowered to legislate by proclamation.

In the old system of real property law in England, fines, levied with "proclamations", i.e., with successive public announcements of the transaction in open court, barred the rights of strangers, as well as parties, in case they had not made claim to the property conveyed within five years thereafter (acts 1483-1484 and 1488-1489). These proclamations were originally made sixteen times, four times in the term in which the fine was levied, and four times in each of the three succeeding terms. Afterwards the number of proclamations was reduced to one in each of the four terms. The proclamations were endorsed on the back of the record. The system was abolished by the Fines and Recoveries Act 1833.