Omišalj (Italian: Castel Muschio; German: Moschau) is a small coastal town in the north-west of the island of Krk in Croatia. The population of the town itself is 1,790 (2001), while the Omišalj municipality also includes the nearby Njivice, bringing the total up to 2,998 people.

Omišalj is one of the oldest towns on Krk, dating from the 3rd century, when it was built by the Romans and named Fulfinium. The town was built on the cliff overlooking the bay of Kvarner, some 80 meters above sea level. It is the site of an early Christian basilica. The town was referred to in the 12th century as "Castri musculi": this is from the Latin Ad musculi meaning "the place of shells".

Omišalj is best known in modern times for hosting the Rijeka international airport as well as an oil terminal.