Depending on nationality, foreigners arriving in Istanbul may need to purchase tourist visas (USA and some EU citizens, depending on exact nationality, do). As of May 2013 the Turkish government has launched the e-Visa system in which you can apply and pay for your visa online and print it out at home prior to your trip to avoid waiting in line at the visa desk at the airport.
If an invitation letter is required in order to request your visa as a visitor, please send the following* to firstname.lastname@example.org:
1. Your registration number (URN) after free online registration
2. The completed Invitation Letter Request Form
3. A photo copy of your passport
*Please note that incomplete requests will not be processed
If you have any remaining visa-related questions, please contact email@example.com