The senior degree of the peerage
A dukedom is the highest of the five degrees of the peerage, and the rarest. The first English dukedom was created in the fourteenth century, and dukes have always stood slightly apart from the ranks below them: they are the only peers whose rank is used as a conversational form of address, and the only ones whose envelope form begins His Grace rather than The.
The peerage of the United Kingdom has five degrees, in descending order: duke, marquess, earl, viscount and baron. Every one of them is addressed differently in speech, in the opening of a letter and on an envelope, and the differences are not decorative — they are the practical shorthand by which a correspondent shows they know which office or dignity they are writing to.
The word Lord is not used for a duke. Lord [Title] is the style of a baron, viscount, earl or marquess; a duke stands above that convention, and addressing him as Lord [Title] is a clear error rather than an informality.
Royal dukes and non-royal dukes
A royal duke is a member of the Royal Family holding a dukedom. He is addressed as a member of the Royal Family, not as a peer: Your Royal Highness on first address, then Sir. The envelope reads His Royal Highness The Duke of [Place]. Your Grace is not used for a royal duke, and the difference is not a nicety — it is the difference between two entirely separate systems of address.
The Royal Household's own guidance is that there are no obligatory codes of behaviour when meeting a member of the Royal Family, only conventions many people prefer to observe. A bow of the head or a curtsy is customary and entirely optional; a handshake is unremarkable. The same latitude does not extend to the words used, where Your Royal Highness followed by Sir remains the settled form.
A non-royal duke — the great majority — is Your Grace and then Duke. If you are unsure which you are dealing with, the presence of His Royal Highness in any published reference settles it immediately.
Speaking to a duke
On a formal first address, say Your Grace. Thereafter, and in almost all ordinary conversation, say Duke. Many dukes will say at once that Duke is quite enough, and taking them at their word is the courteous response rather than a lapse.
Duke is used alone, without the title: Duke, not Duke of Sandford, and certainly not Your Grace repeated through a conversation. The pattern mirrors the way one addresses a bishop or an ambassador — the formal style opens the exchange, and the short form carries it.
Written correspondence
For ordinary letters and emails, open Dear Duke and close Yours sincerely. For strictly formal correspondence — an official approach, a petition, a first letter on institutional business — open Your Grace and close Yours faithfully. Both are correct; the choice signals the register of the letter, and the register should match its content.
In the body of the letter, refer to the recipient as Your Grace in the formal register and as Duke in the ordinary one, and do not mix the two within a single message.
The envelope and invitations
The envelope reads His Grace the Duke of [Place], with decorations following the name. For a royal duke, His Royal Highness The Duke of [Place], with the definite article capitalised, which is the settled royal convention. A non-royal couple is The Duke and Duchess of [Place].
Place cards read The Duke of [Place] and The Duchess of [Place], or in an informal setting simply Duke and Duchess. An invitation to a duke and duchess is addressed jointly and does not extend by style to their children, who hold styles of their own.
The duchess, and the children of a duke
The wife of a duke is a duchess, addressed as Your Grace on formal first address and Duchess thereafter, with Her Grace the Duchess of [Place] on an envelope. A woman holding a dukedom in her own right is extremely rare; where it occurs she is addressed identically, and her husband takes no style from her title.
The eldest son of a duke uses his father's most senior subsidiary title — commonly a marquessate or an earldom — as a courtesy title. Younger sons are Lord [Forename] [Surname], and daughters are Lady [Forename] [Surname]. These are the courtesy lords and ladies discussed in the companion guide to the style of Lord, and none of them holds a peerage while the duke lives.
Context and edge cases
A dowager duchess is styled the Dowager Duchess of [Place], or increasingly [Forename], Duchess of [Place], particularly where a current duchess exists. A divorced wife similarly takes [Forename], Duchess of [Place]. Scottish dukedoms follow the same conventions, with the additional complication that some holders bear Scottish territorial designations of separate origin.
Where a duke holds an office of state or an ecclesiastical or judicial appointment, that office governs correspondence in its own sphere. Where he is addressed socially, the ducal form resumes.
The Barony of Brattleby is a title of honour recorded in The London Gazette and historically associated with Brattleby in Lincolnshire. It is not a property, estate or visitor attraction, and no such claim is made anywhere in this guide.