Sikkim is strict in its policy of arrivals for foreigners, unlike other states (except states like Arunachal Pradesh and other states with International borders) in India. Sikkim has its north-eastern borders touching China and is also a major military base for India.

If you are a foreign national visiting Sikkim, then please make sure that you have a "Inner line permit" to enter Sikkim. These permits are issued on arrival on the land borders of Sikkim - most popular is "Rangpoo Check Post". Foriegn visitors are expected to have these either on their visa itself that reads -'permitted to enter (west Sikkim, east Sikkim) areas of Sikkim'. Or altenately visitors can have these stamped on the border check posts. They are relatively hassel free and can be obtained in a few minutes time.

Travellers might find 'Sikkim Permit' to be filled with confusion when they are initially applying for it along with the visa, but applying this at the spot is easier. You'll be required to go to the check post, show your passport, fill in a form on where you expect to visit for example Pelling, Yuksum, Gangtok, Kewzing etc) and then the authorities will issue you the permit. Permits can also be obtained and they are issued from all Indian missions, Tourism Office located in New Delhi, Sikkim Tourism Office, Calcutta and Sikkim Tourism Office, Siliguri on the strength of an Indian Visa.

Initially Foreigners are issued  a permit for initial period of 15 days duration on the spot without any delay once presented with valid photocopies of Passport and Visa details along with two passport photos of applicants. It can be extended for further 30 days of 15 days each. The extension of permits then is the jurisdiction of Foreigners Registration Office(FRO), Gangtok and Superintendent of Police of North, South and West Districts, again a fairly easy process.

The Office of Foreign Registration (FRO) is located at Kazi Road, Gangtok and direction can be asked to anyone in gthe town.

Exception: The only exception is to visit North Sikkim and Tsangu Lake - If you wish to visit North Sikkim or 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.  If you're making a day trip to Tsangu Lake then a special permit will need to be organised through the agent/vehicle that is driving you across to the place (relatively easy but you'll need to give agents/drivers 24 hours notice period so they can organise this for you (minimal extra cost).

Important: RAP and PAP is only issued to local travel agents affiliated to the local tourism board. Also ensure that you stamp your passport in all the checkposts in Sikkim while travelling (the drivers are well versed with these check posts).