Select committees scrutinise the work of the government by holding inquiries and producing reports on matters of public policy.
They determine their own subjects for inquiry, and have the power to invite submissions of written evidence and call people who can offer a particular insight on the investigation to testify at hearings in Parliament.
Their findings are then published and may be debated in the Commons, the Lords or in Westminster Hall.
The role of most House of Commons select committees is to mirror government departments and examine their spending, policies and administration.
This departmental system of select committees was established in 1979 - but select committees have played an important role in parliamentary scrutiny for many centuries.
Current Commons select committees that do not shadow government departments include the Public Accounts Committee, which scrutinises public spending, and the Administration Committee, which analyses how the House is run.
Another very important committee is the Standards and Privileges Committee which examines allegations of misconduct against individual MPs.
Lords and joint committees
Select Committees in the House of Lords do not mirror government departments but instead focus on specialist subject areas.
The four major Lords select committees hold investigations on science and technology, economic affairs, the UK constitution, and the work of the European Union.
Lords select committees are able to draw on the expertise of some members of the upper House.
There are also joint committees - made up of a mixture of MPs and peers - such as the Joint Committee on Human Rights.