Traveling abroad has become a little more difficult with new regulations taking place since incidents like 9/11. Different countries have their own requirements for you to be issued a visa. Some states only require you to have a passport, two photo id and an application form. For some countries the requirement can be a long list of pay slips to travel accommodations.
Requirements are based on nationality and the country you intend to travel to. Also considered are the type of visa being applied (eg, travel, business, studies, etc.); different rules for each visa. Some of the rules only for certain populations. You can check out India eVisa Online Application for getting more information about online visa services.
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If you are a student and a local university in the country you are traveling to have extended an invitation for you to study there, then you can apply for a study visa. For example, you study in France you'll get a French visa that will allow you to study there. visa will only be valid for the course or courses you are taking.
Business visa requires that you have an invitation from a company in the country you are traveling to. The amount of documentation required can be much more. You may need to provide a letter from the company, proof of paycheck, proof of travel insurance and travel accommodations. Some countries require airlines and hotel reservations made before applying for a visa.