Except for citizens of certain Eastern Bloc and CIS countries, visas are required by everyone to visit Armenia. On arrival you will be granted a 3 week visa, which costs $30. Shorter stays may only require a 3 day transit visa, which can also be granted upon entry, and costs $20. If you wish to obtain the visa before arrival, you can contact your nearest embassy, or else visit the website of the Armenian Foreign Ministry. These cost between $50 and $60. Overstaying your visa will incur a penalty of $3 per day.
Note: It is recommended that you check the latest visa and passport requirements with your embassy before planning a trip to Armenia. These rules are subject to changes very often.