The Limfjord is a shallow part of the sea, located in Denmark where it has been regarded as a inlet ever since Viking times. However, it now has entries both from the North Sea and Kattegat, and hence separates the North Jutlandic Island from the rest of the Jutland Peninsula. The Limfjord extends from Thyborøn Channel on the North Sea to Hals on the Kattegat. It is approximately 180 kilometres long and of an irregular shape with numerous bays, narrowings, and islands, most notably Mors, and the smaller ones Fur, Venø, Jegindø, Egholm and Livø. It is deepest at Hvalpsund.

The North Jutlandic Island, Vendsyssel-Thy, or Jutland north of the Limfjord is the northernmost part of Denmark and of Jutland. It is more common to refer to the three traditional districts of Vendsyssel, Hanherred, and Thy. The area has been intermittently a tied island and, during modern times, was not surrounded by water until a storm in February 1825, which severed the region from the remainder of Jutland and caused a water connection between the North Sea and the western end of the Limfjord. Hence, it is traditionally regarded as a part of Jutland rather than a separate island.