Södertälje Municipality (Södertälje kommun) is a municipality in Stockholm County in east central Sweden. Its seat is located in the city of Södertälje.
It borders to Lake Mälaren in the north and the Baltic Sea in the south, and within the Stockholm County to Nykvarn Municipality and Salem Municipality and also border Södermanland County and its municipals Gnesta and Trosa.
Södertälje also has the fifth largest number of Finnish-speaking Sweden Finns in Sweden: 11,000, or around 13 per cent of the city population. Thus, taken together, Finns and Estimated 120,000 Assyrians/Syriacs in Sweden and account for 40 per cent of the inhabitants of the city.
The municipality was created 1967–1971 through the amalgamation of the former City of Södertälje with large rural and suburban areas surrounding it. In 1999, it was split when a new entity, Nykvarn Municipality, was detached from Södertälje Municipality.