India is currently implementing the world’s largest biometric identification programme: the nationwide Unique Identification Number (UID) system. The project aims to provide biometric IDs to all Indian residents, a total of more than 1.2 billion people. The eventual successes and challenges of the Indian project are likely to have an important influence on the development of national ID programmes in other countries. This policy brief examines legal and policy challenges related to national biometric registration and the forming of a biometric database. What are the challenges and lessons to be drawn from the Indian ID project?