Swedish is closely related to and often mutually intelligible with Danish and Norwegian. Danish and Norwegian are somewhat more similar to each other than either is to Swedish. All three languages diverged from Old Norse about a millenium ago.
Swedish is written using a twenty-nine letter alphabet: the standard twenty-six-letter Roman alphabet plus the additional letters Å / å, Ä / ä, and Ö / ö. These letters are sorted in that order following z. Since Danish and Norwegian names and loan words sometimes appear in Swedish texts, the foreign letters Æ / æ and Ø / ø also occur. Centuries ago, an early form of Swedish was written using the runic alphabet, but its usage has been completely replaced. With respect to inflection, Swedish has five different kinds of nouns and four different kinds of verbs.
The Swedish Academy maintains an official definition of the Swedish language.
The Swedish spoken in Finland, "Finlandssvenska", differs from the Swedish "rikssvenska" mostly in pronunciation.