All travellers need a visa to enter India. There are three types of visas for tourists, available from Indian Consular Offices around the world: the 15-day single/double entry visa, the 90-day visa, or the longer multiple-entry visa for six months. There are certain places in India that are restricted areas which require special permits. These areas include Sikkim, the Northeastern states, Andaman and Nicobar Islands and Lakshwadweep.
Business visas are valid for one or more years with multiple entries. A letter from a sponsoring organization indicating nature of business, duration of stay, and places/companies to be visited is most often required in order to attain this visa.
For more information please contact the Indian consulate closest to you or visit the Embassy of India online.