Košice is the largest city in eastern Slovakia. It is situated on the river Hornád at the eastern reaches of the Slovak Ore Mountains, near the border with Hungary and Ukraine. With a population of approximately 230,000, Košice is the second-largest city in Slovakia, after the capital Bratislava.

Being the economic and cultural centre of eastern Slovakia, Košice is the seat of the Košice Region and Košice Self-governing Region, it belongs to the Košice-Prešov agglomeration, and is home to the Slovak Constitutional Court, three universities, various dioceses, and many museums, galleries, and theatres. In 2013, Košice was the European Capital of Culture, together with Marseille, France. Košice is an important industrial centre of Slovakia, and the U.S. Steel Košice steel mill is the largest employer in the city. The town has extensive railway connections and an international airport.

The city has a preserved historical centre which is the largest among Slovak towns. There are heritage protected buildings in Gothic, Renaissance, Baroque, and Art Nouveau styles with Slovakia's largest church: the Cathedral of St. Elizabeth. The long main street, rimmed with aristocratic palaces, Catholic churches, and townsfolk's houses, is a thriving pedestrian zone with boutiques, cafés, and restaurants. The city is known as the first settlement in Europe to be granted its own coat of arms.

The first written mention of the city was in 1230 as "Villa Cassa". The name probably comes from the Slavic personal name Koš, Koša → Košici (Koš'people) → Košice (1382–1383) with the patronymic Slavic suffix "-ice" through a natural development in Slovak (similar place names are also known from other Slavic countries). In Hungarian Koša → Kasa, Kassa with a vowel mutation typical for the borrowing of old Slavic names in the region (Vojkovce → Vajkócz, Sokoľ → Szakalya, Szakál, Hodkovce → Hatkóc, etc.). The Latinized form Cassovia became common in the 15th century.

Another theory is a derivation from Old Slovak kosa, "clearing", related to modern Slovak kosiť, "to reap". According to other sources the city name may derive from an old Hungarian first name which begins with "Ko".

Historically, the city has been known as Kaschau (in German), Kassa (in Hungarian), Kaşa (in Turkish), Cassovia (in Latin), Cassovie (in French), Cașovia (in Romanian), Кошице (in Russian, Ukrainian, and Rusyn), Koszyce (in Polish), קאשוי (Kashoy) (in Yiddish), and more. Below is a chronology of the various names:

Kingdom of Hungary 1000–1526
John Zápolya's Eastern Hungarian Kingdom 1526–1551 (Ottoman vassal)
Hajduk rebels of István Bocskai 1604–1606 (Ottoman-backed)
Principality of Transylvania (Ottoman vassal) 1619–1629, 1644–1648
Kuruc rebellion 1672–1682 (Ottoman-backed)
Imre Thököly's Principality of Upper Hungary (Ottoman vassal) 1682–1686
Francis II Rákóczi's insurrection 1703–1711
Kingdom of Hungary (crownland of the Austrian Empire) 1804–1867
Austro-Hungarian Empire 1867–1918
Czechoslovakia 1918–1938
Kingdom of Hungary 1938–1945
Czechoslovakia 1945–1992
Slovakia 1993–present

The first evidence of habitation can be traced back to the end of the Paleolithic era. The first written reference to the Hungarian town of Košice (as the royal village of Villa Cassa) comes from 1230. After the Mongol invasion in 1241, King Béla IV of Hungary invited German colonists (see Zipser Germans, Germans of Hungary) to fill the gaps in population. The city was in the historic Abaúj County of the Kingdom of Hungary.