The ability to prove one's identityis increasingly recognized as the basis for participation insocial, political economic and cultural life. Yet at least abillion people in developing countries lack any form ofofficially recognized ID. This problem disproportionallyimpacts rural residents, poor people, women, children andother vulnerable groups in Africa and Asia. Digitalidentity, combined with the extensive use of mobile devicesin the developing world, offers a transformative solution tothis global challenge and provides public and private sectorentities with efficient ways to reach the poorest and mostdisadvantage. This discussion paper, divided into threeparts, explores the connection between digital identity andsustainable development. Part I illustrates how theuse ofdigital identity promotes efficiency gains, financialsavings, social inclusion and access to basic services andrights, with examples from countries that have adopteddigital identity systems. The paper then outlines some ofthe key risks and challenges that must be overcome,specifically in the areas of political commitment, dataprotection and privacy, cost, and sustainable businessmodels. Part II of the paper lays out the digital identitylifecycle and the roles of public and private sectorplayers, and suggests some key considerations in the designof business models. Finally, Part III of the paper suggestssome common principles – including universal coverage,appropriate and effective design, and privacy and dataprotection – and enablers for maximizing the potential ofdigital identity to contribute to sustainable development.