The Kattegat (Danish: [ˈkʰætəkæt]; Swedish: Kattegatt [ˈkâtːɛˌɡat]) is a 30,000 km² (12,000 sq mi) sea area bounded by the Jutlandic peninsula in the west, the Danish Straits islands of Denmark and the Baltic Sea to the south and the provinces of Bohuslän, Västergötland, Halland and Skåne in Sweden in the east. The Baltic Sea drains into the Kattegat through the Danish Straits. The sea area is a continuation of the Skagerrak and may be seen as a bay of the North Sea, but in traditional Scandinavian usage, this is not the case.

The Kattegat is a rather shallow sea and can be very difficult and dangerous to navigate because of the many sandy and stony reefs and tricky currents, which often shift. In modern times, artificial seabed channels have been dug, many reefs have been dredged by either sand pumping or stone fishing, and a well-developed light signaling network has been installed, to safeguard the very heavy international traffic of this small sea.

There are several large cities and major ports in the Kattegat, including, in descending size, Gothenburg, Aarhus, Aalborg, Halmstad and Frederikshavn.