The criteria for membership in the Commonwealth of Nations, which apply to current and prospective member states, have been altered by a series of documents issued over the past eighty-two years.

The 2009 Commonwealth Heads of Government Meeting was the 21st Meeting of the Heads of Government of the Commonwealth of Nations. It was held in Port of Spain, Trinidad and Tobago, between 27 and 29 November 2009, and was hosted by that country's Prime Minister, Patrick Manning.