Foreigners Entry Formalities:
Visa & Permits : In addition to an Indian visa, foreigners must obtain Inner Line Permit (ILP) to visit Sikkim. The permits can be obtained from all Indian missions, Tourism Office, New Delhi, Sikkim Tourism Office, Calcutta and Sikkim Tourism Office, Siliguri on the strength of an Indian Visa.

Foreigners are issued  a permit for initial period of 15 days duration on the spot without any delay provided photocopies of Passport and Visa details along with two passport photos of applicants are made available then and there. It can be extended for further 30 days of 15 days each. The extension of permits can be obtained from  Foreigners Registration Office (FRO), Gangtok and Superintendent of Police of North, South and West Districts.
The  FRO is located at Kazi Road, Gangtok. Phone no  223041

For those interested in going for trekking in the interior regions of the state, you also require a Restricted Area Permit (RAP) OR Protected Area Permit(PAP) which is obtainable in Gangtok from the Police Check Post and Department of Tourism  which is available for certain specified area for groups consisting of 4 or more foreigners subject to the condition that the trekking program is arranged through a registered travel agency.