Summary: The close interrelation between sintering and grain growth is discussed critically, and the necessity for control, but not suppression, of grain growth is established. A distinction between discontinuous and exaggerated grain growth is drawn, and the superiority of grain boundary films as grain-growth control agents is demonstrated. Work on the establishment of tentative criteria for the selection of grain-growth control additives for alumina is reviewed and discussed, and the extension of these ideas to the selection of NaF as a successful aid for magnesia is described.