If a parliament consists of both a lower house and an upper house, all-party parliamentary groups can usually include members of both houses. In the Parliament of the United Kingdom, for example, APPGs include members of the House of Commons and the House of Lords. APPG members meet together, relatively informally, to discuss a particular issue of concern. APPGs are either country based, e.g., the APPG on Zimbabwe, or subject based, e.g., the APPG on breast cancer - the topics reflecting parliamentarians' concerns. APPGs generally have officers drawn from the major political parties and strive to avoid favouring one political party or another. Inevitably, they tend to focus most on the governing party's priorities, discussing new developments and inviting government ministers to speak at their meetings. APPGs have no formal place in the legislature, but are an effective way of bringing together parliamentarians and interested parties. In the UK and many other countries, APPGs must be registered every parliamentary year and must hold an annual general meeting where the Chair and Officers of the area elected.
APPGs allow campaign groups, charities, and other non-governmental organisations active in the field to become involved in discussions and influence politicians. Often a relevant charity or other organisation will provide a secretariat for the APPG helping to arrange meetings and keeping track of its members. Examples of this include Survival International acting as secretariat for All-Party Parliamentary Group for Tribal Peoples; Humanists UK acting as secretariat for the All Party Parliamentary Humanist Group; the APPG on Christianity being administered by a staff member from the Bible Society; or Housing Justice administering the All-Party Parliamentary Group on Homelessness and Housing Need. Other APPGs may resolve their administration burden in other ways, either by borrowing capacity from an MP or peer's office, or by employing staff of their own. The All-Party Parliamentary Group on Freedom of Religion or Belief, for example, employs two members of staff paid for through subscriptions from its stakeholders. The APPG on Agriculture and Food for Development uses a similar model. Other APPGs may have less stringent administrative needs, such as the UK parliament's All Party Parliamentary Jazz Appreciation Group.
As of 2015 there were more than 550 APPGs . The latest official register of APPGs was updated on 2nd May 2017, which shows more than 630 APPGs . Every APPG must hold two meeting during its reporting year, one of which must be an Annual General Meeting (AGM) or a meeting which involves an inaugural election of officers .
In early 2016 the Registrar of Consultant Lobbyists launched an inquiry into concerns that APPGs were being used to bypass lobbying registration rules, following reports that lobbyists were acting as APPG secretariats so gaining access to legislators.
In the Parliament of the United Kingdom, an associate parliamentary group is similar to an all-party parliamentary group except that it is made up of not only members of the House of Commons or Lords but can also include members from outside Parliament.