The Croatian National Theatre Ivan pl. Zajc in Rijeka (Croatian: Hrvatsko narodno kazalište Ivana pl. Zajca Rijeka), commonly referred to as HNK Zajc, is a theatre, opera and ballet house located in Rijeka.

In its rich history theater in Rijeka changed its name several times. After the Municipal (Teatro Comunale), the Theatre was renamed, in 1913, to Teatro Verdi. However, do to historical and political circumstances (the city of Rijeka, at the time known as Fiume, became a Free State before passing to the Kingdom of Italy in 1924) the Croatian language and Croatian theater artists did not have access to the theater at all until the end of 1945 when, following the example of similar permanent national domestic and foreign theatrical institutions established permanent National Theatre in Rijeka, the Croatian drama, Italian drama and opera and ballet. On October 20, 1946, after passing to Yugoslavia, a show played on its stage in the Croatian language for the first time. It was Ivan Gundulić's Dubravka, directed by Dr. Matko Foteza with Marija Crnobori in the role of Dubravka. It was soon followed by the first performance of an opera and ballet, Zajc's Nikola Subic Zrinjski, conducted by Boris Papandopulo, and the title role sung Milan Pichler. The first play of the Italian drama was Goldoni's Il burbero benefico. In the year 1953 the theater gets a new name after another one composer, but this time the biggest Croatian and a fellow citizen of Rijeka, Ivan Zajc.

Since 1991 theater got the status of national theater, and in 1994 its present name, Croatian National Theatre Ivan pl. Zajc. From the historical 1946 to today, with its four artistic branches (Croatian Drama, Italian Drama, the Symphonic Opera and ballet) and more than 50 years of their continuous operation, with its quality performance HNK in Rijeka managed to set high theatrical and artistic criteria and placed itself on the rightful place of one of the by quality leading theaters in Croatia. At the same time, his repertoire today is characterized by performances of drama, opera and ballet classics as well as works of Croatian dramatic and operatic heritage and also first performances of the national acts, especially contemporary.

All the major Croatian theaters were built in the second half of the 19th century, including the one in Rijeka - behind Osijek (1865), and before Split (1893) and Zagreb (1895).