People have been queued through the state of Assam to check that their name is on the National Register of Citizens.
India publishes the final version of a list that practically takes about 1.9 million people in the northeast
Families are required to provide documentation to show their ancestry and those who cannot prove their nationality are considered illegal aliens.
India says that the process is necessary to identify illegal migrants from Bangladesh.
BBC correspondent for South Asia Rajini Vaidyanathan was in Katajar village to meet with some of the people who said they were at risk.