According to the recent visa regulations, Schengen country citizens and CIS citizens are not required to have a visa. The above mentioned citizens can stay on the territory of the Republic of Armenia for no more than 180 days during one year. 

Check here for the list of countries that do not need an entry visa for Armenia: http://www.mfa.am/u_files/file/consulate/Visa/visafreelisteng2.pdf

In all other cases foreign citizens are obliged to obtain a visa for entering Armenia. A visa can be obtained from the Armenian consulate if available in your country, by e-Visa (electronic visa application) or upon arrival at the airport or borders of Armenia. The charges of a visa for a single visit in Armenia up to 21 days is 3000 AMD (approx. € 6).  

See here for more information about the visa regulations in Armenia.