A national census is under way in India with the aim of creating a biometric database by photographing and fingerprinting everyone over the age of 15.
The government will use the information to issue identity cards and classify India's population of 1.2 billion by gender, religion, occupation and education.
It's India's 15th census - they are done once every 10 years - but the first with a biometric element has been included.
The first person to be listed, President Pratibha Patil, appealed to fellow Indians to follow her example "for the good of the nation".
"Everyone must participate and make it successful," she said in Delhi.
The exercise faces big challenges, not least India's vast area and diversity of cultures. Officials must also contend with high levels of illiteracy and millions of homeless people - as well as insurgencies by Maoists and other rebels.