All foreign nationals entering India are required to possess a valid international travel document in the form of a national passport with a valid visa obtained from an Indian Mission or Post abroad.

Please contact Indian Embassy/High Commission/Honorary Consuls of India for any information related to visa processing. Please find the link to the Indian Missions Abroad.
https://conference.mha.gov.in/NOC_letter.pdf ( download NOC letter)

In case of certain countries visa will not be required if the delegate of any these countries hold diplomatic or official passport. The list of countries is available on the website of Ministry of External Affairs.
http://www.mea.gov.in
http://mea.gov.in/visa-exemption.htm