The letter "Å" is often perceived as an "A" with a ring, interpreting the ring as a diacritic mark. However, the ring is not a diacritic. Rather, the letter developed as a form of semi-ligature of two consecutive "A"s. The letter represents a sound which according to historical linguistics has the same origin as the long /A:/ sound in German Aachen and Haar (Danish and Norwegian hår, English hair).
It has been used in Scandinavian languages since medieval times when the futhark was exchanged for the Latin alphabet. Although it was abandoned in Danish and Norwegian due to German influence, it has been retained in Swedish. The letter was re-introduced in Norwegian in 1917 and in Danish in 1948. The letter is also used in the Chamorro language.
In Danish and Norwegian languages, "Aa" is considered equivalent to "Å", in as much as "Aa" is the old spelling, and a fully functional transcription for "Å" when using a foreign typewriter. In surnames, and occasionally in names of geographical places, the old spelling with "Aa" is retained. Correct alphabetisation in Danish and Norwegian places "Aa" along with "Å" as the last letter in the alphabet.
In the Swedish alphabet, "Å" is sorted immediately after "Z", as the third letter from the end. In the Finnish alphabet, the letter is treated just as in Swedish, but its usage is limited to Swedish names.
In the Norwegian, Danish and Swedish languages, å is even an entire word, meaning a rivulet, a stream or a small river, like the rivers Aa, Au and Aue on the European continent.
For computers, when using the ISO 8859-1 or Unicode sets, the codes for "Å" and "å" are respectively 197 and 229, or C5 and E5 in hexadecimal. In HTML character entity references, required in cases where the letter is not available by ordinary coding, the codes are Åand å. Unicode also allows code 8491 (212B in hexadecimal) when the letter is used specifically as a symbol for the ångström, but 197 is preferred.
The letter "Å" is also used throughout the world as the international symbol for the non-SI unit angstrom, or ångström, a physical unit of length named after the Swedish physicist Anders Jonas Ångström. It is always upper case in this context.