As of 2015, U.S. citizens must have a visa to enter Turkey. U.S. citizens traveling to Turkey for tourism or commerce must get an e-visa, which they can purchase online. For any other type of travel, travelers must purchase visas in advance.
E-visas purchased in advance online cost $20, and e-visas purchased in Turkish airports cost $30. When traveling to Turkey for tourist or commercial purposes, U.S. citizens can stay in Turkey for 90 days within a 180-day period.
Travelers must purchase visas for other types of travel through a Turkish Embassy or Consulate in advance. A one-year, single-entry visa purchased through an embassy or consulate costs $60, and a five-year, multiple-entry visa costs $200, as of 2015.