Seals were widely used by statesmen, nobles, judiciaries, the church, and even ordinary men and women as a means of proving that the accompanying document had been written or approved by them. This was particularly important during the Middle Ages when most of the population could not read or write. Using a seal in this way gave rise to the term "seal of approval", which we still use today.

Seals were also used to literally "seal" documents ensuring their privacy - rather like arabic gum on an envelope today. The Great Seal was the most important of all seals as it was used by the monarch to sanction public acts and edicts. It was therefore a very powerful political tool and the monarch would appoint a trusted official to act as "Keeper of the Seal".

Edward III used seven or eight Great Seals during his reign, with changes incorporated to reflect his claims to the throne of France. The example shown here is the so called Br‚tigny seal which was used between 1360 and 1369 and has been described by Allan Wyon as "the culminating point of excellence in the design and execution in the series of Gothic Great Seals of England". It was engraved after the Treaty of Br‚tigny in 1360, when Edward renounced the title King of France, and continued in use until June 1369, when he resumed the title.

Despite this technical renunciation, it is significant that, although he dropped the legend Rex Francie et Anglie (King of France and England) for Rex Anglie : Dominus Hibernie et Acquitannie (King of England : Lord of Ireland and Acquitaine), he retained the arms of France on the quarters of his shield.