All international tourists visiting Bhutan with the exception of visitors from India, Bangladesh and Maldives must have a visa to visit Bhutan. 

Indian, Bangladeshis and Maldivian nationals can obtain a permit at the port of entry on producing a valid passport with a minimum of 6 months.
All other tourists must obtain a visa clearance prior to their travel to Bhutan. Visas are processed through an online system by your tour operator in Bhutan on your behalf.  For which you are required to send the photo-page of your passport to us and we shall then apply for your visa. the visa will be processed by the Tourism Council of Bhutan (TCB) upon verification of the full payment of your tour plus USD $40 visa fee. Once verified, your visa will be processed within 72 working hours.

You are then required to show your visa clearance at the port of entry which will then be stamped on to your passport.