Only citizens of the following countries can travel to Iran without a visa: Azerbaijan, Bolivia, Ecuador, Georgia, Malaysia, Nicaragua, Turkey, and Venezuela. However, visa status is subject to change at any time so always check with your nearest embassy prior to planning a trip. US citizens require a special visa and must travel with a government-approved guide throughout their visit. You can consult the State Department website for the most up-to-date travel information here:

Health and Safety

Visitors should be aware that medical facilities are not up to western standards in the cities, let alone in the rural areas. It is recommended that you purchase airlift health insurance, which allows travelers to be flown to the closest international hospital, usually in Germany or Austria, in case of emergency.

Visitors should be vaccinated against typhoid and polio prior to traveling to Iran. Tap water is generally not drinkable so you're advised to buy bottled water and avoid ice. Up-to-date health issues in Iran and recommendations can be found on the World Health Organization website:

There are specific threats to western travelers, as they might be targeted by gangs and criminals, especially outside the capital. It is best not to drive yourself and use a travel agency with transportation and a guide. Visitors are strongly recommended to stay away from the borders areas, especially those with Afghanistan and Iraq. Terrorism is a general threat and you should always stay away from large public gatherings or demonstrations. The political situation is subject to change at any time so keep the phone number of your embassy on hand and check for government-issued alerts whenever possible.

Visitors should also be aware that the government does in some cases track western travelers. This means that phone conversations may be monitored. Always be careful what you say on the phone or in public, especially about the government or Islam. 

As Iran is a strict Muslim country, visitors should always respect local customs and dress conservatively. Showing affection in public is frowned upon and should be avoided. Photography in public places can be tricky, as the government does not allow pictures of military and government buildings. Since it is sometimes difficult to ascertain what a building is, not photographing it is the best way to stay out of trouble.