All visitors are required to carry a passport valid at least for the next 6 months. Visa exemptions include:

Bhutanese and Nepalese visitors who are staying for less than 3 months,

Nationals from the Maldives, if they are staying for a maximum of 90 days (this includes any periods they may have spent in India up to 6 months prior to the visit in question),

Transit passengers who have a follow-on ticket within 72 hours of arrival as long as they are not going to leave the airport.

Special restrictions apply to Pakistani and Afghan nationals.
Its always wise to check updated visa requirements prior to travel.