For many countries entry into Doha requires a visa. There are two types, a transit visa (for visits between 5 and 96 hours) or a single-entry visa valid for one month.
The transit visa is free to travellers that are transiting through Qatar via Qatar airlines. This has been implemented in a bid to start promoting Qatar as a reasonable transit hub, and to boost tourism of the region.
Kiwi Roamer, the less intrepid traveler 