Lord Warden of the Cinque Ports (Latin: Dominus Custos Quinque Portuum) is the name of a ceremonial post in the United Kingdom. The post dates from at least the 12th century, when the title was Keeper of the Coast, but it may be older. The Lord Warden was originally in charge of the Cinque Ports (/sɪŋk pɔːrts/ sink ports), a group of five (cinque in Norman French) port towns on the southeast coast of England formed to collectively supply ships for The Crown in the absence of a formal navy at that time. Today, the post is a sinecure and an honorary title, and 14 towns belong to the Cinque Ports confederation. The title is one of the higher honours bestowed by the Sovereign; it has often been held by members of the Royal Family or by prime ministers, especially those who were influential in defending Britain in times of war.

The Lord Warden was solely responsible for the return of all writs to the Crown, along with the collection of taxes and the arrest of criminals. His court was held in St James's church, near Dover Castle, and there he exercised jurisdiction broadly equivalent to that of Chancery. He also had a "lieutenant's powers of muster". The Constableship of Dover Castle, later added (1267) to the warden's office, enabled him to keep a garrison and administrative staff, including the clerk and the lieutenant of the castle.

The coat of arms of the Cinque Ports is first recorded in 1305 (and is probably a few years older), predating even the arms of the City of London. The arms comprise a shield divided per pale (vertically), depicting on the dexter side (viewer's left) three gold half lions passant gardant on a red field; and on the sinister side (viewer's right) three gold half ships' hulls on a blue field. These arms are also flown as an heraldic banner (flag); and (with additional elements indicating the individual office-holder) form the basis of the banner of the Lord Warden.

The creation and appointment of the Lord Warden, once among the most powerful appointments of the realm, by the Sovereign was instituted principally after the portsmen sided with the Earl of Leicester against King Henry III, in the Second Barons' War, and was intended to provide some central authority over the Cinque Ports, which were essentially otherwise independent of the King's sheriffs. It was combined from 1267 with the office of Constable of Dover Castle. However, from 1708 Walmer Castle at Deal was to be preferred as the official residence of the Lord Warden of the Cinque Ports. The Lord Warden also holds the office of Admiral of the Cinque Ports with a maritime jurisdiction extending to the middle of the English Channel, from Redcliffe near Seaford, in Sussex, to the shore underneath the Naze Tower, encompassing Brightlingsea in Essex, the only Cinque Port north of the Thames. In earlier centuries the northern limit was taken as the Shoe Beacon in Essex.

The courts of Brodhull and Guestling were established to protect the privileges of the Cinque Ports by the portsmen themselves. From the 15th century these courts had been largely replaced by the Lord Warden's Court at Dover. From the 16th century the principal business of the courts was the installation of the Lord Warden and the court is now only occasionally summoned. The office continued to be a powerful one. In 1550 the Mayor and Jurats of Dover refused to accept a Royal Writ because it was not accompanied by a letter of attendance from the Lord Warden. The member ports' parliamentary representatives were appointed by the Lord Warden at first; despite an act passed in 1689 to curb this influence, it continued until the 19th century.

At the installation of a new Lord Warden, the Speaker of the Confederation of the Cinque Ports instructs the Lord Warden: "to undertake the duties of the Ancient and Honourable Office and to uphold the Franchises, Liberties, Customs and Usages of the port."

The office of Speaker has traditionally rotated between the affiliate townships every year dating from at least 1550. Inaugurations are begun on 21 May, and membership is ordained through a longstanding maritime tradition of a principle of the prevailing winds coming from west to east.

A unique uniform is specified for the Lord Warden (though those appointed to the office in the 21st century have, as retired admirals, worn naval uniform instead). The uniform is very similar to a pre-1956-pattern Admiral's uniform (complete with cocked hat) trimmed in red and with Cinque Ports insignia. Sir Winston Churchill's uniform (pictured) is preserved at Chartwell; Sir Robert Menzies's uniform (pictured), which he wore as Lord Warden from 1966 to 1978, is preserved at the National Library of Australia.