Nogometni klub Osijek, commonly referred to as NK Osijek or simply Osijek, is a Croatian professional football club from Osijek. Founded in 1947, it was the club from Slavonia with the most seasons in the Yugoslav First League and, after the independence of Croatia in 1992, it is one of the four clubs that have never been relegated from the Croatian First League, the others being Dinamo Zagreb, Hajduk Split and Rijeka.

Osijek is the fourth-largest city in Croatia, with a population of 96,848 in 2021. It is the largest city and the economic and cultural centre of the eastern Croatian region of Slavonia, as well as the administrative centre of Osijek-Baranja County. Osijek is on the right bank of the Drava River, 25 km (16 mi) upstream of its confluence with the Danube, at an elevation of 94 m (308 ft).