This chapter explores new organisational forms of co-operative and mutual enterprise that have developed in twenty-first century Britain in the context of public sector reform and the state’s retreat from service provision. It notes the roots of these ‘new mutuals’ in the concepts of co-operation and mutuality developed in the nineteenth century and analyses the ideas, operational practices and organisational structures they use. Citing examples in health care and housing provision, they explore the growth of multi-constituency organisational forms among new mutuals. Finally, the chapter analyses the opportunities and challenges facing such organisations in seeking to mainstream mutuality in public services.