Marne-Nordsee is an Amt ("collective municipality") in the district of Dithmarschen, in Schleswig-Holstein, Germany. Its seat is in Marne. It was formed on 1 January 2008 from the former Amt Kirchspielslandgemeinde Marne-Land, the town Marne and the municipality Friedrichskoog.

The Amt Marne-Nordsee consists of the following municipalities (with population in 2005):

1. Diekhusen-Fahrstedt (734)
2. Friedrichskoog (2.522)
3. Helse (964)
4. Kaiser-Wilhelm-Koog (364)
5. Kronprinzenkoog (965)
6. Marne (6.018)
7. Marnerdeich (341)
8. Neufeld (646)
9. Neufelderkoog (144)
10. Ramhusen (163)
11. Schmedeswurth (215)
12. Trennewurth (269)
13. Volsemenhusen (368)

53°57′00″N 9°00′00″E / 53.950°N 9.000°E / 53.950; 9.000