Since Estonia joined Europe (EU) in 2004. EU citizens, Americans, Australians, Canadians, and New Zealanders do not need visas to visit.
However if you do need one, you at least have the consolation that an “Estonian visa” is valid throughout most of Europe as Estonia is now in the Schengen area. Equally if you have started your tour in another Schengen country, the visa it issued is valid for Estonia too.
Check the Estonian Ministry of Foreign Affairs website if you are in any doubt. It is always up to date with visa information and gives details of Estonian embassies abroad where they can be obtained.
Visas used to be issued at Tallinn Harbour and from the consular section of Estonian Embassy at Tallinn Airport. This is no longer the case, so if you need one, make sure you get it before you come. If you are getting it en route, make sure you allow enough time and that your visit there does not coincide with any national holidays. It is best to book an appointment with the consular section in advance.