Immigration check is done for all passengers, Indians or foreigners, both at the time of arrival and departure. All overseas passengers on arrival at New Delhi International airport are required to fill in an 'Arrival Card' for immigration/customs clearance, similarly when departing from New Delhi a 'Departure Card' has to be filled.

Delhi International Airport Private Limited offers a unique immigration experience to all departing & arriving passengers. In order to provide smooth and fast immigration at IGI Airport, a large number of immigration desks have been deployed at the new terminal 3. These desks have clear demarcation for various categories. These categories are

Passengers with special needs
Business Class / First Class Passengers
Passengers with Indian Passport
Passengers with Foreign Passport
Passengers of Indian Origin/ Overseas Citizen of India
Diplomats/ Officials
Passengers from SAARC Nations

For further details on immigration requirements, please visit
http://www.immigrationindia.nic.in/
http://www.immigrationindia.nic.in/Instr_foreigners2.htm