Aadhaar (English: foundation or base) is a 12-digit unique identity number that can be obtained voluntarily by residents or passport holders of India, based on their biometric and demographic data. The data is collected by the Unique Identification Authority of India (UIDAI), a statutory authority established in January 2009 by the government of India, under the jurisdiction of the Ministry of Electronics and Information Technology, following the provisions of the Aadhaar (Targeted Delivery of Financial and other Subsidies, benefits and services) Act, 2016.]
Aadhaar is the world's largest biometric ID system. World Bank Chief Economist Paul Romer described Aadhaar as "the most sophisticated ID programme in the world". Considered a proof of residence and not a proof of citizenship, Aadhaar does not itself grant any rights to domicile in India. In June 2017, the Home Ministry clarified that Aadhaar is not a valid identification document for Indians travelling to Nepal and Bhutan.