The Limfjord (Danish: Limfjorden [ˈliːmˌfjoːˀɐn]) is a shallow sound in Denmark that separates the island of Vendsyssel-Thy from the rest of the Jutland Peninsula. It 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 (24 metres).

Its main port is Aalborg, where a railway and a road bridge are built across the Limfjorden to Nørresundby, while motorway E45 passes it through a tunnel to the east. Commercial ports also exist at Thisted, Nykøbing Mors, Skive, Løgstør, Struer, Lemvig and Thyborøn. There are also bridges at Oddesund, Sallingsund, Vilsund, Aggersund and Sebbersund, and a number of ferry crossings.

At its western end, a sand isthmus of shifting proportions has separated the Limfjord from North Sea during historic times. The present inlet, Thyborøn Channel, has existed only since 1862, turning the northern part of Jutland into an island. An passage also existed during the Viking age. Based on placenames and the geography it is thought to have been to the south of the present one, between Ferring Sø (locally still called 'the Fjord') and Hygum Nor. Canute the Great sailed into it in 1027 on his way back from England. According to Saxo Grammaticus it closed at some time around 1200. There are records of several floods piercing the isthmus during the 16th to early 19th century.