common changes to the Germanic vowel *a, a plural form -as, and a number of other features which make scholars believe they form a distinct group within West Germanic.

It is debated whether the shared features of North Sea Germanic are inherited from a common proto-language or formed through later contact and influence. Additionally, the membership of the group is sometimes debated. Some scholars exclude Low German for lacking a number of features associated with North Sea Germanic. Other scholars include Dutch for sharing some features