The Marmara Region forms a passage between the Balkan Peninsula and Anatolia. Europe and Asia are connected to each other in this region. It covers 8.5 percent of the country with a surface area of 67,000 km2. It gets its name from the internal sea with the same name, which is entirely surrounded by land and connected to the Black Sea and the Aegean Sea through the straits. The islands of Bozcaada and Gokceada (Imroz), situated in the open sea off the Aegean coast, are also located in the Marmara Region.

The Marmara Region is surrounded by the Black Sea and Central Anatolia Regions to the east, the Aegean Region to the south and Greece and Bulgaria to the northwest. The borders of the Marmara Region are not in conformity with the provincial borders in many places just as in the other regions. Edirne, Kirklareli, Tekirdag, Istanbul, Kocaeli and Yalova Provinces are completely within the borders of the region. Some lands in Sakarya, Bilecik, Bursa, Balikesir and Canakkale Provinces are located within the borders of the Aegean and the Black Sea Regions.