Not all the work in Parliament is done in an adversarial manner. Parties co-operate too, and much inter-party co-operation takes place through what are known as 'All-Party' committees or groups. These groups are relatively informal compared with other parliamentary activity, and groups come and go according to the interests of MPs. In some cases groups are set up after lobbying from interests outside Parliament. Members receive information about these groups through the All-Party Notices, drawn up and issued by the Government Whips every Thursday. This includes information about forthcoming meetings
There are just over 500 groups, the members of which mainly include backbench Members of the House of Commons and Lords, although they may include Ministers and even people outside Parliament. There is an Approved List (compiled and maintained by the Office of the Parliamentary Commissioner for Standards) of groups that comply with certain basic requirements, and most groups are included on this list. Groups that are not included are given a lower priority for room bookings, are not advertised in the All-Party Notices, and may not style themselves as "All-Party", "Associate", or " Parliamentary" groups. Groups have to re-register after each general election.
There are two types of All-Party Group: those that focus on particular countries and those that are concerned with substantive subjects (policy areas or particular activities). There are around 380 subject groups and nearly 130 country groups. For a complete list see the Register of All-Party Groups. For the rules governing these groups see Guide to the Rules on All-Party Groups. See also Dod's Guide to All Party groups
Many groups have their own websites. The following is not a complete list of groups, but represents links to those websites that I have been able to find, plus one or two that aren't official websites but provide useful information about the work of the group.