Every visitor to Turkey must have a valid passport and a visa if required. 108 countries all around the World may visit Turkey without long visa procedures.
For official visa procedure, visitors could also visit the official webpage of the Ministry of Foreign Affairs / Visa web page. (http://www.mfa.gov.tr/visa-information-for-foreigners.en.mfa)
E-Visa application is possible from any place. The whole process takes an average of 3 minutes.
More details can be found at www.evisa.gov.tr