Citizens from more than 150 countries can apply for an e-Visa (www.indianvisaonline.gov.in/evisa).
You must apply a minimum of four days and a maximum of 120 days before you are due to arrive in India.
The visa will be valid from your date of arrival in India.
It's a double-entry visa that lasts for 60 days from your first date of entry.
To apply, upload a photograph as well as a copy of your passport; have at least 180 days' validity in your passport and at least two blank pages.
If your application is approved, you will receive an attachment to an email within 72 hours (though normally much sooner), which you'll need to print out and take with you to the airport. You'll then have the e-Visa stamped into your passport on arrival in India.
Note that the e-Visa is also sometimes referred to as a 'visa on arrival', though you need to apply for it before you arrive.
E-Visas are only valid for entry through 26 designated airports (Ahmedabad, Amritsar, Bagdogra, Bengaluru, Calicut, Chennai, Chandigarh, Cochin, Coimbatore, Delhi, Gaya, Goa, Guwahati, Hyderabad, Jaipur, Kolkata, Lucknow, Madurai, Mangalore, Mumbai, Nagpur, Pune, Trichy (Tiruchirappalli), Thiruvananthapuram (Trivandrum), Varanasi and Visakhapatnam).
They are also valid for arrival at five designated seaports (Cochin, Goa, Mangalore, Mumbai and Chennai).
E-Visa holders can, however, leave India from any authorised immigration checkpoint.