When traveling to Istanbul, you should remember that there are varied requirements for entry into Turkey, depending on what country you are from:
For Americans, Canadians, Australians and Irish Nationals: You must have a valid US passport and visa. At the point of entry, you need to present a visa. Most visas issued would be valid for three months and may either be single entry only (for Americans) and multiple entry (for Canadians, Australians and Irish nationals). This can be obtained upon your entry to the country.
For UK Nationals: You must have a valid UK passport. If you are a British Citizen or an Overseas British National (living in Hong Kong), visas can be obtained upon entry and are valid up to three months, multiple entry.
Upon entry, your passport will be checked to make sure that it is valid at least until the period of your stay in Istanbul and any other part in Turkey. The customs officer will also check if you have tickets onward to another destination or return tickets. Also, they will check that you have enough money to support your stay in the country. The fee for the visa is about 20 US dollars. It will also be helpful to note that many a traveler has been denied entry because they looked unkempt. So it is best to keep a neat appearance.
There are also citizens from countries where Turkey has an agreement and these nationals do not need a visa to enter the country. For a three-month stay, nationals of the following countries only need a valid passport: Argentina, Bulgaria, Andorra, Chile, Bolivia, El Salvador, Japan, Israel, Denmark, Finland, Germany, Ecuador, Greece, Honduras, Iceland, Liechtenstein, Switzerland, Singapore, South Korea, Nicaragua, Morocco, Monaco, Luxembourg, Malaysia, Iran, New Zealand, Sweden, Trinidad and Tobago, Northern Cyprus, Vatican City, Venezuela, Tunisia and San Marino. Meanwhile, nationals of Macedonia, Croatia and Bosnia-Herzegovina don’t need a visa for a two-month stay – a valid passport will do. Nationals from Macau, Kirghizstan, Costa Rica and Kazakhstan also need only a valid passport, but only for stays of until one month. Note that as of this writing, Turkey is not yet a part of the European Union.
When entering Turkey, you may bring personal items without having to pay duties. However, some items are only limited to one unit per person – video players, portable radio/cassette/CD player, camera with up to five rolls of film, a pair of binoculars, a typewriter and other items specified in the Turkish Embassy website. For obvious reasons, you are not allowed to bring drugs into the country, as well as weapons and other sharp instruments.
When leaving Turkey via Istanbul, you should be able to show receipts for the purchases you made. That way, you can easily declare your items. Carpets are charged with duties, but some that are antiques will not be allowed to be taken out of the country. This also goes for porcelain, ancient coins and other items. If you really want to bring home an authentic antique, you will have to have it authenticated by a museum official and a permit is needed for its exportation.