The 1999 İzmit earthquake was a magnitude 7.6 earthquake which struck the Kocaeli Province of Turkey on 17 August 1999. Between 17,127 and 18,373 people died as a result, and it caused an estimated US $6.5 billion in damage. It was named for the quake's proximity to the northwestern city of İzmit. The earthquake occurred at 03:01 local time at a shallow depth of 15 km. A maximum Mercalli intensity of X (Extreme) was observed. The earthquake lasted for 37 seconds, causing seismic damage, and is widely remembered as one of the deadliest natural disasters in modern Turkish history.

İzmit is a municipality and the capital district of Kocaeli Province, Turkey. Its area is 480 km2, and its population is 376,056 (2022). The capital of Kocaeli Province, it is located at the Gulf of İzmit in the Sea of Marmara, about 100 km (62 mi) east of Istanbul, on the northwestern part of Anatolia. Kocaeli Province had a population of 2,079,072 inhabitants in 2022, of whom approximately 1.2 million lived in the largely urban İzmit City metro area made up of Kartepe, Başiskele, Körfez, Gölcük, Derince and Sapanca. Unlike other provinces in Turkey, apart from Istanbul, the whole province is included within the municipality of the metropolitan center.