This, actually, is a really intricate question. In India, there are lots of different kinds of visa, for example for tourists, businessmen, journalists, and investigators. International interns come to India on many different kinds of visa: Indian E Tourist Visa Online, Entry Visa, Employment Visa, Business Visa or Student Visa, not one of those being applicable to most internship situations. 

The Entry Visa (X Visa) is normally for those whose purpose of visit India doesn't fit into some of the typical visa categories, like people coming for short-term classes, volunteer work, or unpaid internships into India. You need to apply for an Entry Visa and a copy of the offer letter saying the conditions of your internship place. If you're a student and the internship is part of the research you also need to acquire a letter from the college describing why you're likely to E Visa India.

Internships using a "stipend", allowance or wages are usually thought to be paid internships and those technically require an Employment Visa (which requires additional documentation like the employment contract along with also a evidence from the employer which no formal Indian federal could be utilized to fill the place). But many organisations may directly request that you come to a Tourist Visa since it is simpler for them and also for the applicant - despite the fact that it's technically legal.

Before applying for all types of visa be certain your passport is valid for 6-18 months, depending upon your specific visa. Applicants that are not citizens within their nation but taxpayers have to send a copy of their residence permit with this program. It's always a good idea to seek advice from the various embassy in your own country, for instance the Indian embassy in Spain, Germany, Italy etc.. There you may find the majority of the information considering your visa.