A fingerprint scan, an eyescan, and a headshot photo are being taken for every Indian right now. The database started out as a voluntary program before becoming mandatory.
The "biometric identification program" called "AADHAR" now has 1.15b people in its database -- 99% of all Indian adults are documented.
Many Indians don't otherwise have birth certificates or other documentation. There is also a lot of fraud and theft related to identity (not just with crossing borders and regular crime, but also with the government's attempts to send money to assist the poor) in the country of many uneducated people.
Now in India every bank account and tax return must be linked to a person's biometric ID, and an AADHAR is required to receive any government benefits. According to the government, this is expected to save India around $11b per year.
The project cost the equivalent of $1.5b dollars, and was undertaken in the name of security as well as order, including monitoring border-crossers between Indian and Pakistan and Bangladesh.
There is criticism. Rights groups say the savings are not as great as the government claims, and fraud can still go on because a middle man whose role it is to confirm AADHAR and distribute government welfare can still deny resources or engage in corrupt behavior. There have already been leaks of personal data as well.
The country's supreme court has confirmed the right of the government to link AADHAR to social benefits and tax returns, but hasn't yet ruled on whether the state can force Indians to register without violating his right to privacy.