Aadhaar, which means "foundation" is a unique 12-digit identity number issued to all residents of India based on their biometric and demographic data. The data are compiled by the Unique Identification Authority of India (UIDAI), a statutory authority established in January 2009 by the Government of India, under the Ministry of Electronics and Information Technology, in accordance with the provisions of the Aadhaar (Target Delivery of Financial and other Subsidies, benefits and services) Act of 2016.
Aadhaar is the world's largest biometric identification system, with more than 1,171 million subscribers as of August 15, 2017. As of this date, more than 99% of Indians over 18 years of age had been enrolled in Aadhaar . World Bank chief economist Paul Romer described Aadhar as "the most sophisticated identification program in the world."
Prior to the enactment of the Act, UIDAI served as an adjunct office of the Planning Commission (now NITI Aayog) since January 28, 2009. On March 3, 2016, a money bill was introduced in Parliament for legislative support to Aadhaar. On March 11, 2016, the Aadhaar (financial services and other subsidies, benefits and services) Act of 2016 was approved at Lok Sabha. On March 26, 2016, this Law was notified in the Gazette of India .
Aadhaar is a proof of residency and not a proof of citizenship. It does not grant any right of domicile in India. In June 2017, the Ministry of Interior clarified that Aadhaar is not a valid identification document for Indians traveling to Nepal and Bhutan.