Kronstadt (Кроншта́дт), also spelled Kronshtadt, Cronstadt (Krone for Crown and Stadt for City) is a Russian seaport town, located on Kotlin Island, thirty kilometers west of Saint Petersburg near the head of the Gulf of Finland. It is under the administration of the federal city of Saint Petersburg and is also its main port. In March 1921 it was the site of the Kronstadt rebellion.

Traditionally, the seat of the Russian admiralty and the base of the Russian Baltic Fleet were located in Kronstadt guarding the approaches to Saint Petersburg . The historic centre of the city and its fortifications are part of the World Heritage Site Saint Petersburg and Related Groups of Monuments.