A courtesy title is a form of address in systems of nobility used for children, former wives and other close relatives of a peer, as well as certain officials such as some judges and members of the Scottish gentry. These styles are used "by courtesy" in the sense that persons referred to by these titles do not in law hold the substantive title. There are several different kinds of courtesy titles in the British peerage system.

Marquess of Lansdowne is a title in the Peerage of Great Britain created in 1784, and held by the head of the Petty-Fitzmaurice family. The first Marquess served as Prime Minister of Great Britain.