Two different women, one word
The word baroness covers two quite different positions, and almost every avoidable error in this area comes from collapsing them. A baroness in her own right holds the peerage herself: she was created a life peer, or she succeeded to a hereditary barony that could descend to a woman. The wife of a baron holds no peerage at all; she has a courtesy style derived from her husband's dignity and it ends if the marriage ends.
In speech the two are addressed identically as Lady [Title], which is why the distinction is so easily lost. It reappears the moment something is written down, because the envelope form differs, the way she is listed in a programme differs, and the way her children and husband are styled differs.
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.
Speaking to a baroness
Say Lady [Title]. This is correct for a peeress in her own right and for the wife of a baron, and it is what you will hear used at receptions, in committee corridors and in ordinary professional exchange. Baroness [Title] is not wrong, but in conversation it sounds like a caption rather than an address, and it is not how most holders introduce themselves.
As with every British style, restraint is the rule. Use the style once when you first speak to her, then continue naturally. Repeating Lady [Title] in every sentence draws attention to the speaker rather than the person addressed.
Your Ladyship is not a general-purpose address. It survives in a small number of formal and institutional contexts and, used casually, will read as pastiche.
Written correspondence
Open Dear Lady [Title]. That form serves for a letter, an email and a printed note, and it is appropriate whether the recipient is a life peer, a hereditary peeress or a baron's wife. Close with Yours sincerely. For an entirely formal approach where you have no acquaintance — a petition, a submission, an approach to a peer in her parliamentary capacity — Dear Madam with Yours faithfully remains correct.
Within the letter, refer to her as Lady [Title]. If you must use the full form because the letter will be read by others, Baroness [Title] is appropriate in the body and in any accompanying biographical note. A programme entry, an order of proceedings or a speaker list conventionally uses Baroness [Title].
The envelope and invitations
For a baroness in her own right, write The Baroness [Title]. If she is a Privy Counsellor, The Rt Hon. the Baroness [Title]. Post-nominal letters follow the name. Some peeresses prefer The Lady [Title] on envelopes; where a known preference exists, the preference wins, because forms of address exist to serve the person addressed and not the other way round.
For the wife of a baron, the envelope reads The Lady [Title]. A couple invited together is The Lord and Lady [Title]. Where the peeress holds the title and her husband does not, the invitation is addressed to The Baroness [Title] and Mr [Surname] — his name follows hers, which is the correct order of precedence and not, as it is sometimes read, a discourtesy.
Formal introduction
The presenting formula is May I present Baroness [Title]. Here the full style is used deliberately: an introduction is one of the few spoken moments where the rank itself is being conveyed to the listener, so the more formal word is the useful one. Thereafter, conversation reverts to Lady [Title].
Courtesy styles and what they are not
A courtesy style is a form of address a person is entitled to use socially without holding the underlying dignity. The wife of a baron holds one; so do the sons and daughters of senior peers. It confers no peerage, no parliamentary right and no legal privilege, and it is worth being precise about that in biography and in press material, where the two are frequently blurred.
The husband of a peeress receives no reciprocal courtesy style. There is no male equivalent of Lady [Title], and there never has been. Inventing one — or describing a peeress's husband as a lord — is the error most likely to be noticed by anyone familiar with the peerage.
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 this guide makes no claim to the contrary.
Context and edge cases
A divorced wife of a baron may, by convention, continue to use the style [Forename], Lady [Title] — the forename before the style signals that she is no longer the wife of the current holder. A widow becomes the Dowager Lady [Title], or more commonly today [Forename], Lady [Title], particularly where a younger Lady [Title] now exists.
Women who hold judicial or ecclesiastical office, or an office of state, are addressed by that office in its own context, and the peerage style resumes socially. Where two styles compete, the working rule is that the office governs while she is acting in it, and the peerage governs otherwise.