Suburban trains are running on three metropols of Turkey: Istanbul, Izmir and Ankara.
Suburban system is under construction in two cities: Gaziantep and Kayseri. Suburban train of Balikesir is on paper. Suburban train of Adapazari (Adaray) is suspended.
Marmaray (Istanbul)
Marmaray is 77-km-long suburban system connecting one end of Istanbul to the other. It connects two sides of Istanbul (thus Asia and Europe) via Marmaray tunnel under Bosphorus.

As of 13th of March, Marmaray trains started service from Halkali to Gebze crossing Istanbul and Bosphorus.
Izban (Izmir)
136-km-long Izmir suburban line (Izban) is the longest and busiest suburban system in Turkey. The network will reach to 185 km after Aliaga-Bergama strech is commissioned.

Izban is succesfully integrated with metro, tram and bus services. It’s possible to reach to airport, even to Selcuk where Ephesus is located.
Baskentray (Ankara)
37-km-long suburban system of Ankara, Baskentray, had been commissioned in 2018 after renewal works.

Baskentray trains cross Ankara from Kayas in one end to Sincan in the other. Suburban trains are also calling at Ankara high speed train station. It’s possible to interchange metro from suburban trains.