Most travelers need an e-Visa. It takes 10 minutes online, costs $35-50 depending on passport, and lasts 180 days. Here's the short version.
Citizens of EU countries (most), UK, Japan, Singapore, South Korea, Brazil, Argentina, Russia, and Ukraine can enter visa-free for up to 90 days. Bring a passport valid for at least 6 months from entry.
US, Canada, Australia, UAE, Saudi Arabia, and many others need an e-Visa. Apply at the official site: evisa.gov.tr. Fill in passport details, pay by card, get a PDF within minutes.
Important: only use the official evisa.gov.tr site. Third-party 'visa services' charge 2–4x more for the same form.
A small number of nationalities (including Nigeria, some African countries) may still need a sticker visa. Check your country's Turkish consulate page — or apply for the e-Visa first; it covers more countries than people realize.
Airside transit in Istanbul (IST or SAW) doesn't require a visa. Leaving the airport does.
This is a practical guide, not legal advice. Always check your own government's travel page and the Turkish consulate site before booking non-refundable flights.
Activate these from home — cheaper and simpler than sorting them at the airport.