Mors or Morsø is an island in the shallow sound called Limfjorden within Denmark's Jutland peninsula. It has an area of 367.3 km2 and as of 1 January 2019, it had a population of 20,373. The main town on the island is called Nykøbing Mors. Geologically Mors is unique. Like the neighbouring island of Fur, it is known for its deposits of diatomite, locally known as 'moler' (mo-clay).

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.