Unlike the elected House of Commons, all members of the House of Lords (excluding 90 hereditary peers elected among themselves and two peers who are ex officio members) are appointed. The membership of the House of Lords is drawn from the peerage and is made up of Lords Spiritual and Lords Temporal. The Lords Spiritual are 26 bishops in the established Church of England. Of the Lords Temporal, the majority are life peers who are appointed by the monarch on the advice of the Prime Minister, or on the advice of the House of Lords Appointments Commission. However, they also include some hereditary peers including four dukes.
Membership was once an entitlement of all hereditary peers, other than those in the peerage of Ireland, but under the House of Lords Act 1999, the right to membership was restricted to 92 hereditary peers. As of 2018, only one of them is female (the Countess of Mar); most hereditary peerages can only be inherited by men.
While the House of Commons has a defined 650-seat membership, the number of members in the House of Lords is not fixed. There are currently 793 sitting Lords. The House of Lords is the only upper house of any bicameral parliament to be larger than its lower house.
The House of Lords scrutinises bills that have been approved by the House of Commons. It regularly reviews and amends Bills from the Commons. While it is unable to prevent Bills passing into law, except in certain limited circumstances, it can delay Bills and force the Commons to reconsider their decisions. In this capacity, the House of Lords acts as a check on the House of Commons that is independent from the electoral process. Bills can be introduced into either the House of Lords or the House of Commons. While members of the Lords may also take on roles as government ministers, high-ranking officials such as cabinet ministers are usually drawn from the Commons. The House of Lords has its own support services, separate from the Commons, including the House of Lords Library.
The Queen's Speech is delivered in the House of Lords during the State Opening of Parliament. In addition to its role as the upper house, until the establishment of the Supreme Court in 2009, the House of Lords, through the Law Lords, acted as the final court of appeal in the United Kingdom judicial system. The House also has a Church of England role, in that Church Measures must be tabled within the House by the Lords Spiritual.
Today's Parliament of the United Kingdom largely descends, in practice, from the Parliament of England, though the Treaty of Union of 1706 and the Acts of Union that ratified the Treaty in 1707 created a new Parliament of Great Britain to replace the Parliament of England and the Parliament of Scotland. This new parliament was, in effect, the continuation of the Parliament of England with the addition of 45 MPs and 16 Peers to represent Scotland.
The House of Lords developed from the "Great Council" (Magnum Concilium) that advised the King during medieval times. This royal council came to be composed of ecclesiastics, noblemen, and representatives of the counties of England and Wales (afterwards, representatives of the boroughs as well). The first English Parliament is often considered to be the "Model Parliament" (held in 1295), which included archbishops, bishops, abbots, earls, barons, and representatives of the shires and boroughs of it.