Commonwealth of Nations membership criteria
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 most important of these documents were the Statute of Westminster (1931), the London Declaration (1949), the Singapore Declaration (1971), the Harare Declaration (1991), the Millbrook Commonwealth Action Programme (1995), the Edinburgh Declaration (1997), and the Kampala Communiqué (2007).
Source: Wikipedia — Commonwealth of Nations membership criteria (CC BY-SA 4.0)