The Peerage of the United Kingdom consists of all noble titles created by the Sovereign since the legal unification of the Kingdom of Great Britain and the Kingdom of Ireland on January 1, 1801. It succeeded the Peerages of England, Scotland, Ireland, and Great Britain. Until the passage of the House of Lords Act 1999, membership in this peerage conferred an automatic hereditary right to a seat in the upper house of Parliament, a constitutional privilege that distinguished it from the post-1801 Irish peerage, whose members had to elect representative peers to sit at Westminster.
Heraldic and social precedence within this peerage is determined strictly by the grade of the title—Duke, Marquess, Earl, Viscount, or Baron—and thereafter by the date of the letters patent. In the modern era, since the Life Peerages Act 1958, the vast majority of new creations within this peerage have been non-hereditary baronies, representing a significant shift from feudal tenure toward a meritocratic system of legislative service. Despite this, the Peerage of the United Kingdom remains the primary vessel for the continuation of the British honors system and the formal hierarchy of the realm.