The vast majority of international flights come to Tehran. However, some travellers are choosing to start or end their trip in Shiraz, saving some backtracking.
Tehran’s Imam Khomeini International Airport (IKIA) sees most of Iran’s international air traffic. It’s small, so delays are possible. Elsewhere, Shiraz, Esfahan, Mashhad, Tabriz, Bandar Abbas and Kish (in that order) are potentially useful arrival or departure points, while Abadan, Ahvaz and Zahedan are less useful.
Iran Air is the national airline and has the Homa, a mythical bird, as its symbol. As the government-owned carrier, it offers service with an Islamic flavour (ie no pork, no alcohol and no exposed hair on the hostesses).
Note that Caspian Airlines, Kish Air and Taban Air have all had fatal crashes in the past 10 years.
All airlines are based in Tehran except for Taban Air, which is in Mashhad.
Caspian Airlines Damascus, Dubai, İstanbul, Kyiv, Yerevan
Iran Air Amsterdam, Ankara, Baku, Beijing, Beirut, Cologne, Copenhagen, Damascus, Doha, Dubai, Frankfurt, Gothenburg, Hamburg, İstanbul, Karachi, Kuala Lumpur, Kuwait, London, Milan, Mumbai, Paris, Stockholm, Tashkent, Vienna
Kish Air Damascus, Dubai, İstanbul
Mahan Air Almaty, Baghdad, Bangkok, Birmingham, Damascus, Delhi, Dubai, Dusseldorf, İstanbul, Kabul, Kuala Lumpur, Phuket, Shanghai
Taban Air International flights to cities in Central Asia and the Middle East
Air Arabia Sharjah
Air Asia Malaysia
Air India Delhi
Ariana Afghan Airlines Kabul, Mazar-e Sharif
Austrian Airlines Vienna
Azerbaijan Airlines Baku
Etihad Airways Abu Dhabi
Kuwait Airways Kuwait City
Lufthansa Frankfurt, Munich, Zürich
Qatar Airways Doha
Saudi Arabian Airlines Jeddah, Riyadh
Syria Air Damascus
Tajik Air Dushanbe
Turkish Airlines İstanbul
Buying tickets in Iran for flights from Iran is best done through an agent – you can only buy tickets online if you're using an Iranian credit or debit card. The Middle East is a popular staging point, with several airlines connecting Tehran, Esfahan and Shiraz to the world via various Gulf airports. East and Southeast Asia also have quite a few services, but there are no direct flights from North or South America. Instead, most people come through Europe, where a host of airlines have regular flights to Tehran, or the Middle East.
Departure tax is included in the price of a ticket.