While planning your trip to Islamic Republic of Iran do not forget to check your passport if it is valid for at least 90 days. Valid Iranian visa required and depending on your nationality most probably your stay as a tourist is limited up to 3 months (for one entrance). To be safe, start the visa process at least two months before you plan to arrive.
Note that all applications stall over the Norooz holiday period, therefore, submit before 8 March to be sure.
Passport-holders from Bosnia-Herzegovina, Macedonia, Saudi Arabia, Singapore, Slovenia and Turkey get a three-month tourist visa on arrival. Iran usually issues 15-day tourist visas on arrival (Airport Visa) to people from about 65 countries, including most European, ASEAN, Gulf Arab and Central Asian countries, several South American countries, Australia, China, India, Japan, New Zealand and South Korea.