Nacka is the municipal seat of Nacka Municipality and part of Stockholm urban area in Sweden. The municipality's name harks back to a 16th-century industrial operation established by the Crown at Nacka farmstead where conditions for water mills are good. However, and somewhat confusingly, that spot is not densely populated and the municipal seat is on land that once belonged to Järla farmstead on the other side of Lake Järla.

Nacka Municipality (Nacka kommun) is a municipality in Stockholm County in east central Sweden. Its seat is located at Nacka. The municipality is situated just east of the capital Stockholm and the western parts are considered a suburban part of the Stockholm urban area.

The present municipality was created in 1971 when the City of Nacka (itself instituted in 1949) was amalgamated with Saltsjöbaden (itself detached from "old" Nacka in 1909) and Boo.

The municipality is situated in two historical provinces (landskap), Uppland and Södermanland, but in one administrative county (län), Stockholm County.

The western densely built-up area of Nacka Municipality is a contiguous part of the Stockholm urban area. About 50,000 of the municipality's total population live there.

There are also some more localities in the municipality. The larger ones are: Boo, Fisksätra, Saltsjöbaden, Skuru and Älta.

The area has been populated since the first mountaintops emerged as islands from the sea after the end of the last Ice Age, during the Mesolithic. During the Viking Age (800 – 1100 AD) the area has been estimated to have been populated by 100 people. They were living by farming and fishing.