Frogn is a municipality in Akershus county, Norway.

Frogn is located at the southern part of the peninsula between the main Oslofjord and Bunnefjorden.

The municipality (originally the parish) is named after the old Frogn farm (Old Norse: Fraun), since the first church was built here.

The arms symbolize the Oscarsborg Fortress in silver on a blue background.

The fortress was built in the late 19th century and played a major role in the defence of Norway in the beginning of World War II.