All tourists (excluding Indian, Bangladeshi and Maldivian passport holders) who wish to travel to Bhutan require a visa and must book their holiday through a Bhutanese tour operator or one of their international partners. The tour operator will take care of Visa arrangements for visitors. A listing of licensed Bhutanese tour operators can be found at the link below. 

Comprehensive list of Tour Operators: https://www.bhutan.travel/tour-operators