Tourists from over 33 countries - including the USA, Canada, Germany, and Iceland - can obtain a tourist visa upon arrival at the airport.
Other nationalities needs to arrange this before hand, either through a travel agent, a hotel or even Qatar Airways.
For work permits and business visas, the local company usually arranges this.
Changes to visa regulations regularly occur on short notice, so look through recent posts in this section.
Make sure to also check with your airline and/or embassy for further information.