Participants from USA, Canada, Japan, China, European Union and former USSR countries can obtain a tourist visa to Turkey upon entry with a valid passport and payment of a fee (i.e., $20 USD for US citizens).

Participants from other countries should check the rules for their own passports with Turkish consulates in their countries.

For more information please take a look at the page
http://www.mfa.gov.tr/default.en.mfa