Before 1225, Old Swedish is chiefly known from runic inscriptions.

The early phase has archaic traits including the preservation of old German diphthongs and the almost complete conjugation of verbs according to person. Changes took place earlier in southern Sweden.

In certain areas, Norrland, Gotland and Finland these old diphthongs are still preserved.

The transition to middle Swedish is usually dated around the end of the fifteenth century.