The Proto-Norse language developed into Old Norse by the 8th century, and Old Norse began to develop into the modern North Germanic languages in the mid- to late 14th century, ending the language phase known as Old Norse. These dates, however, are not absolute, since written Old Norse is found well into the 15th century.
Old Norse was divided into three dialects: Old West Norse, Old East Norse, and Old Gutnish. Old West and East Norse formed a dialect continuum, with no clear geographical boundary between them. For example, Old East Norse traits were found in eastern Norway, although Old Norwegian is classified as Old West Norse, and Old West Norse traits were found in western Sweden. Most speakers spoke Old East Norse in what is present day Denmark and Sweden. Old Gutnish, the more obscure dialectal branch, is sometimes included in the Old East Norse dialect due to geographical associations. It developed its own unique features and shared in changes to both other branches.
The 12th-century Icelandic Gray Goose Laws state that Swedes, Norwegians, Icelanders, and Danes spoke the same language, dǫnsk tunga ("Danish tongue"; speakers of Old East Norse would have said dansk tunga). Another term, used especially commonly with reference to West Norse, was norrœnt mál or norrǿnt mál ("Nordic/Northern speech"). Today Old Norse has developed into the modern North Germanic languages Icelandic, Faroese (both inherited cases from the language), Norwegian, Danish, and Swedish, of which Norwegian, Danish and Swedish retain considerable mutual intelligibility.