Under the reforms of the House of Lords Act 1999, the majority of hereditary peers lost the right to sit as members of the House of Lords, the upper house of the Parliament of the United Kingdom. Section 2 of the Act, however, provides an exception from this general exclusion of membership for up to 92 hereditary peers: 90 to be elected by the House, as well as the holders of two royal offices, the Earl Marshal and the Lord Great Chamberlain, who sit as ex officio members. The initial cohort of excepted hereditary peers were elected in the 1999 House of Lords elections. Between 1999 and November 2002, vacancies among this group were filled by runners-up in the 1999 election. Since then, by-elections to the House of Lords have filled vacancies.
Candidature for both the 1999 elections and subsequent by-elections is restricted to peers in the Peerages of England, Scotland, Great Britain and the United Kingdom. Peers in the Peerage of Ireland are only eligible for election if they hold a title in one of the other peerages, but if successful may use their Irish peerage title as a member of the House. The electorates are either the whole membership of the House of Lords (including life peers), or a party group of sitting hereditary peers. A standing order of the House, approved prior to the commencement of the House of Lords Act 1999, mandates that the 90 elected hereditary peers consist of: