Rijeka (Croatian: Rijeka, Croatian pronunciation: [rijɛ̌ːka]; Italian: Fiume) is the principal seaport and the third largest city in Croatia (after Zagreb and Split). It is located on Kvarner Bay, an inlet of the Adriatic Sea and has a population of 128,735 inhabitants (2011). The conurbation, which includes adjacent towns and municipalities of Opatija, Lovran, Mošćenička Draga, Matulji, Kastav, Viškovo, Klana, Kostrena, Čavle, Jelenje, Bakar, and Kraljevica has a population of 213,842 (2011).

Historically, because of its strategic position and its excellent deep-water Port of Rijeka, the city was fiercely contested, especially between Italy, Hungary, and Croatia, changing hands and demographics many times over centuries. According to the 2001 census data, the overwhelming majority of its citizens (80.39%) are Croats, with Serbs coming in second (6.21%). The Croatian, Slovene and Italian version of the city's name mean river in each of the languages.

Rijeka is the center of Primorje-Gorski Kotar County in Croatia. The city's economy largely depends on shipbuilding (shipyards "3. Maj" and "Viktor Lenac") and maritime transport. Rijeka hosts the Croatian National Theatre "Ivan pl. Zajc", first built in 1765, as well as the University of Rijeka, founded in 1973 but with roots dating back to 1632.