Ö

Ö (lowercase ö) is a letter of extended Latin alphabets, written as an o with two dots above it, used in languages such as German, Swedish, Finnish, Turkish, Hungarian, Icelandic, Estonian, and Dutch.¹ In Unicode it is encoded as U+00D6 for the capital and U+00F6 for the lowercase, both formally named LATIN LETTER O WITH DIAERESIS, in the Latin-1 Supplement block.² The same two dots serve two distinct linguistic purposes depending on the language: as an umlaut, they mark a genuinely different vowel sound; as a diaeresis, they mark that a vowel begins a separate syllable.^{3 • 4}

Umlaut and diaeresis: two roles for one glyph

The two dots over the o are a single character in Unicode, and the same glyph serves both purposes; what changes is the reason the dots are there, and that depends on the language.³ In German, Swedish, and Turkish, the dots mark an umlaut, a genuine change of vowel sound: ö is not an o with decoration but a distinct vowel, roughly the sound in her without the r.³ FrathWiki gives Swedish as an example: plain o represents /u/ while ö represents /ø/.⁴ The Routledge Dictionary of Language and Linguistics describes the umlaut as a diacritic used in German (ä, ö, ü), Swedish (ä, ö), and Icelandic (ö) to mark vowel mutation, a process whose English reflexes survive in plural forms such as mouse becoming mice.⁸ In German orthography, the affected graphemes a, o, and u are written ä, ö, and ü with the umlaut mark, which looks identical to the diaeresis mark.⁹

As a diaeresis (known as tréma in French), the dots do not change the sound value of the letter; they mark that the vowel is not part of a diphthong or digraph.⁴ In languages without the front rounded vowels, the character is known as an "o with diaeresis" and denotes a syllable break, with the pronunciation remaining an unmodified [o].⁵ Some speakers use the term umlaut loosely for a diaeresis, and vice versa.⁹

Unicode names the combining mark U+0308 COMBINING DIAERESIS and uses it in both kinds of spelling, and the precomposed letters such as ä, ö, ü, ë, ï, and ÿ carry the word "diaeresis" in their official names regardless of which purpose they serve.^{6 • 10} The formal name of U+00F6 in the original Unicode 1.0 names list was LATIN SMALL LETTER O DIAERESIS.²

Origins

The two marks have different origins even though modern typography gives them the same shape.⁴ Diaeresis was borrowed from the Greek alphabet.⁴ The umlaut began as a small e placed on top of a, o, or u; that superscript e later evolved into the same shape as the diaeresis, and Buncic's 2023 study of diacritic etymology notes that the resulting two little strokes above the letters were also used in printed blackletter type.^{4 • 11}

Encoding details

U+00F6 sits in the Latin-1 Supplement block, whose letters section is based on ISO/IEC 8859-1 (Latin-1).^{2 • 12} Its canonical decomposition is o followed by U+0308 COMBINING DIAERESIS, so text can be written either with the precomposed character or as a base letter plus combining mark; the two forms are equivalent under Unicode normalization (NFC and NFD respectively).^{2 • 6} The lowercase character maps to uppercase U+00D6 and titlecase U+00D6, encodes in UTF-8 as the two bytes C3 B6, is written left to right, and is not mirrored in bidirectional text.² In matching and identifier contexts, the "o-umlaut" German character at U+00F6 must be treated as clearly different from plain o, and no matching program should yield an "equal" comparison between them.¹³ The European Union's Formex specification lists both Ö and ö with their UTF-8 byte sequences (C3 96 and C3 B6) for Dutch, Estonian, Finnish, German, Hungarian, Icelandic, Swedish, and Turkish.¹⁴

Typing and substitution

Common ways to enter the character include holding Alt and typing 0246 on the numeric keypad (the shorter Alt+148 also works on US English systems using code page 437), typing 00F6 followed by Alt+X in Microsoft Word and Outlook, pressing Ctrl+Shift+: then o in Word, using the dead-key sequence quote-then-o on a US-International keyboard, and searching for the letter in Character Map or Google Docs' special-character picker.¹ In markup and code it can be written as ö or ö in HTML, \00F6 in CSS, and \u00F6 in JavaScript; Google Sheets accepts the formula =UNICHAR(246).⁷

The letter matters in practice because replacing ö with plain o changes the spelling and pronunciation of names and words in languages that use it, such as German and Swedish.¹⁵

References

1. ö o with umlaut: copy and how to type it, Accent Letter
2. ö – U+000F6, decodeunicode.org
3. O With Two Dots: The Umlaut And Diaeresis Explained, O With Accent
4. Diaeresis and Umlaut, FrathWiki
5. U+00F6 LATIN SMALL LETTER O WITH DIAERESIS: ö, Codepoints
6. Diaeresis and umlaut: same dots, different roles, Diacritical Marks
7. ö Latin Small Letter O with Diaeresis – How to Type, Unicode & HTML Code, Symbol Spotter
8. Routledge Dictionary of Language and Linguistics, entries on umlaut
9. What is the difference between a dieresis and an umlaut?, English Language & Usage Stack Exchange
10. Diaeresis vs Umlaut: What's the Difference?, Type This or That
11. Buncic 2023, Etymology of diacritics & origin of Czech diacritics, University of Cologne
12. The Unicode Standard, Version 18.0, code chart U+0080 (C1 Controls and Latin-1 Supplement)
13. J. Klensin, Network Working Group document on character matching
14. Latin letters, EU Vocabularies Formex specification, Publications Office of the EU
15. ö (o with diaeresis), Free Symbols

Topic: Encyclopedia › Society and history › Languages and linguistics › Writing and notation systems › Latin script

Initially written Sep 17, 2026 · Reviewed: Sep 30, 2026; Oct 25, 2026 · Edited: Oct 15, 2026; Oct 25, 2026 · Last review: Oct 25, 2026

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