This is a history of the production and marketing of diamonds from the period of the `rush' to Kimberley and the rise of De Beers to the formation of the Central Selling Organization by South African producers and London and South African merchants. Based on a wide variety of original sources from public and mining company archives, it is both a business and a political study of a South African monopoly which became an international cartel. The Diamond Ring departs from previous histories by emphasizing the key role of the merchants in financing and organizing the trade in opposition to the South African state, as each struggled to gain control of production in the 1920s and 1930s. It explains the reasons for state interest in diamond production and the eventual co-operation of politicians, officials, and diamond magnates in regulating supply and sales. It includes much new material on the ways in which the British government strengthened the hand of the Diamond Syndicate and the Diamond Corporation to maintain and extend central selling beyond South Africa to other states - Zaire, Angola, Ghana, and Sierra Leone - before independence, as the `Ring' expanded into a world-wide brokerage based in London.