A baroness is a woman who holds the title of nobility of baroness, which is the lowest of the five noble classes in the peerage system in Britain. A baroness is equivalent in rank to a baron, and both are members of the House of Lords in the UK Parliament. A baroness can be the wife or widow of a baron, or she can hold the title in her own right. Typically, the title denotes an aristocrat who ranks higher than a lord or knight, but lower than a viscount or count. 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.

When addressing a baroness, one can refer to her as Baroness . The husband of a baroness in her own right gains no title or style from his wife. It is common for the surnames of barons and baronesses to be identical to or included in the formal title of their barony.