Øresund or Öresund (Danish: Øresund, pronounced [ˈøːɐsɔnˀ]; Swedish: Öresund, pronounced [œrɛˈsɵnːd]) is a strait which forms the Danish–Swedish border, separating Sjælland (Denmark) from Skåne (Sweden). The strait has a length of 118 kilometres (73 mi) and the width varies from 4 kilometres (2.5 mi) to 28 kilometres (17 mi). It is 4 kilometres (2.5 mi) wide at its narrowest point between Helsingør in Denmark and Helsingborg in Sweden.
Øresund is one of three Danish Straits that connect the Baltic Sea to the Atlantic Ocean via Kattegat, Skagerrak, and the North Sea, and is one of the busiest waterways in the world.
The Øresund Bridge, between the Danish capital Copenhagen and the Swedish city of Malmö, inaugurated on 1 July 2000, connects a bi-national metropolitan area with close to 4 million inhabitants. The HH Ferry route, between Helsingør, Denmark and Helsingborg, Sweden, in the northern part of Øresund, is one of the world's busiest international ferry routes with more than 70 departures from each harbour per day.