Gebze (Turkish pronunciation: [ˈɟebze]), formerly known as Libyssa, is a municipality and district of Kocaeli Province, Turkey.

[1] It is situated 65 km (30 mi) southeast of Istanbul, on the Gulf of Izmit, the eastern arm of the Sea of Marmara.

Gebze is the largest district by population size in the province as of 2022, exceeding İzmit, the provincial capital.

[1] The district of Gebze is located in the western portion of Kocaeli Province; with neighbors Körfez to the east; Pendik, Tuzla and Şile in Istanbul to the northwest, west and north respectively; Çayırova and Darıca to the southwest and Dilovası to the southeast.

[5] A Marmaray intercontinental commuter rail line connects Gebze to the European side of Istanbul.