No matter where you are from or why you come to Turkey, you will need a valid passport from your country of origin. Your passport should also have at least 90 days validity remaining. Even if your passport is within 6 months of its expiration date, consider renewing it before your trip or move to Turkey.
Whether or not you need a Turkish visa will depend on your country of origin and the length of and reasons for your trip. Many countries have signed Visa Exemption Agreements that allow their citizens to visit Turkey for up to 3 months without a visa. Certain nationalities that are not visa exempt may obtain visas at their point of entry into Turkey (though they will be charged a cash fee). For a list of these countries and their permitted lengths of stay, check with the Turkish Ministry of Foreign Affairs. The Ministry also lists fee amounts on its website.
Make sure you are aware of all your required documentation before you leave for Turkey. If you are travelling to Turkey to live, work, or study, you will require specific permits. A basic guide through the process is listed below:
If you plan on leaving Turkey and returning at some point during your stay (for business or vacation), make sure that you apply for a visa that allows multiple re-entries. If you leave the country and are only eligible for a single entry, you will be refused entry upon your return.
Again, verify all requirements and restrictions with the Turkish embassy or consulate in your country before you submit your application. Ask questions if you are unsure of anything. The immigration process will probably test your patience from time to time, but it is better to confirm information with Turkish officials than make mistakes on your applications.