Christian IV's Arsenal, is a historic building on Slotsholmen in central Copenhagen, Denmark. It was built by Christian IV of Denmark in 1604 as part of a grand scheme for the construction of a new naval harbour. The arsenal, along with several other buildings, surrounded the harbour basin which was connected to the main harbour by a narrow canal. Later, when ships became too large to enter the harbour, the fleet moved to Bremerholm and the decommissioned naval harbour was later filled in.

Slotsholmen is an island in the harbour of Copenhagen, Denmark, and part of Copenhagen Inner City. The name is taken from the successive castles and palaces located on the island since Bishop Absalon constructed the city's first castle on the island in 1167 at the site where Christiansborg Palace lies today.