The British nobility consists of members of the immediate families of peers who bear courtesy titles or honorifics. Members of the peerage carry the titles of duke, marquess, earl, viscount or baron.

Baron is a rank of nobility or title of honour, often hereditary. The female equivalent is baroness. In the Peerage of England, the Peerage of Great Britain, the Peerage of Ireland and the Peerage of the United Kingdom (but not in the Peerage of Scotland), barons form the lowest rank, placed immediately below viscounts.

William I introduced the rank of baron in England to distinguish those men who had pledged their loyalty to him under the feudal system. Previously, in the Anglo-Saxon kingdom of England, the king's companions held the title of earl and in Scotland, the title of thane. All who held their feudal barony "in-chief of the king", that is with the king as his immediate overlord, became alike barones regis ("barons of the king"), bound to perform a stipulated annual military service, and obliged to attend his council.

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