Note: the 2 month gap rule on Tourist visas was abolished in late November 2012.
The following information explains the 2 month gap, when it was in operation.
In order to prevent people from going on visa runs and staying in India continuously on a Tourist Visa, the Indian government introduced a mandatory 2 month gap between visits to India. It doesn't have to spell disaster for your vacation though. If you have a genuine reason for needing to return to India within 2 months on a Tourist Visa, there are a couple of options.
- Apply for a Re-Entry Permit: If you have an urgent need to return to India within 2 months, you can apply for a re-entry permit (stamp in your passport). This can be done at any Indian visa processing center (or directly at the Indian consulate if allowed). What's classed as an urgent need to return to India is subjective. All applications are assessed on a case by case basis, and depending on the documentation provided. There have been many cases where people have been granted re-entry permits in non-emergency situations, so it's worth applying.
- Tourism to Neighboring Countries: If you take a side trip to a neighboring country such as Nepal, Thailand, or Sri Lanka, and you can support it with a detailed printed itinerary and return flight home from India, you can re-enter India within 2 months. Immigration officers have the discretion to allow tourists up to 3 entries, based on need, without a re-entry permit for this kind of travel. If you submit your itinerary when you apply for your visa, you may even get a stamp on your visa waiving the rule. This depends on where you apply though. It's most common in the UK.
Note: Anyone who does re-enter India within 2 months on a Tourist Visa must register at a Foreigner's Regional Registration Office within 14 days.