The Danish Straits are the main connection between the Baltic Sea and the world oceans. The regime of passage through these straits has been the subject of extensive regulation, raising the question how different applicable instruments interact. Apart from applicable bilateral and multilateral treaties, it is necessary to take into account the practice of Denmark and Sweden and other interested states, and regulatory activities within the framework of the IMO. The Case Concerning Passage Through the Great Belt before the ICJ provides insights into the views of Denmark and Finland. The article concludes that an 1857 treaty excludes the applicability of Part III of the LOS Convention to the straits, and that there are a number of difficulties in assessing the contents of the regime of the straits. At the same time, these uncertainties do not seem to have been a complicating factor for the adoption of measures to regulate shipping traffic.