Why does my slugify turn Ærø into just r?

Because the usual trick, NFKD followed by dropping non-ASCII, only works for letters that break down into a base letter plus an accent. Æ and ø have no decomposition, so both get deleted. Map them yourself first (Æ to AE, ø to o) or use a transliteration library: Python's unidecode turns Ærø into AEro.

Is Æ a letter or just a ligature of A and E?

Both, depending on the language. In Danish, Norwegian, Icelandic and Faroese it's a full letter with its own place in the alphabet, after Z in Danish and Norwegian. In English and Latin it's a ligature, so Æsop and Aesop, or encyclopædia and encyclopaedia, are the same word. Only the second group can swap it for ae without misspelling anything.

Is Æ the same letter as Swedish Ä?

Same role, different letter. Danish and Norwegian write the sound with Æ and Ø, while Swedish and Finnish use Ä and Ö, so Bjørn and Björn are one name in two spellings. Unicode keeps them separate and no normalization links them, so a search across Nordic data has to fold Æ with Ä and Ø with Ö itself.

How is Æ written on passports and plane tickets?

As AE. The machine-readable line of a passport follows ICAO rules that spell Æ as AE, with Ø becoming OE and Å becoming AA. Airline booking systems only take A to Z, so enter the name exactly as that line shows it, even though the printed name above it keeps the Æ.

ASCII 198

Uppercase AE ligatureBox T-junction pointing right, double horizontal

ASCII 198 is Æ on Windows and ╞ in old DOS.

Æ (Capital AE) is byte 198 in Windows-1252, Unicode U+00C6. Danish and Norwegian use it as a capital letter (Ærø, Ære), and English keeps it in a few classical spellings like Æsop. It's also a classic test for password migrations. A legacy system that hashed passwords as Windows-1252 bytes saw Æ as the single byte C6, while a UTF-8 system hashes C3 86, so a Danish user with Æ in their password can't log in after the switch even though they type it correctly. Rehash at their next successful login under the old scheme, or check both encodings during the transition. Old DOS had Æ at 146. In UTF-8, C3 86 misreads as Ã†. The HTML entity is Æ.

╞ (Single Vertical, Double Right) is byte 198 in code page 437, the original IBM PC character set, and maps to Unicode U+255E. It's the left-edge tee of a single-line box where a double divider ═ (205) branches off to the right; ╡ at 181 closes the same divider on the right edge. Code page 850 put ã on this byte, so Portuguese text saved in 850 and read as 437 shows the tee in the middle of words: São Paulo becomes S╞o Paulo. In UTF-8 it's E2 95 9E, and the HTML entity is &boxvR;.

Latin LetterBox Drawing

Technical Details

Code Example

</>

#include <stdio.h>

int main(void) {
    /* On Windows (code page 1252) byte 198 is Æ.
       Modern terminals expect UTF-8, so print the code point, not the byte. */
    printf("\u00C6\n");   /* UTF-8: C3 86 */

    unsigned char b = 198;         /* the raw Windows-1252 byte */
    printf("%d 0x%02X\n", b, b);    /* 198 0xC6 */
    return 0;
}

Code Example

</>

#include <stdio.h>

int main(void) {
    /* Byte 198 is ╞ only on a console using code page 437
       (chcp 437 on Windows, or DOSBox). On a UTF-8 terminal the
       lone byte 0xC6 is invalid and prints as garbage, often �. */
    putchar(198);

    /* char is signed on x86, so a plain char holding 0xC6 is -58.
       Use unsigned char when you compare or index by byte value. */
    char c = (char)198;
    unsigned char u = 198;
    printf("\n%d %d\n", c, u);   /* -58 198 */

    /* Portable: print the Unicode character as UTF-8 instead. */
    printf("\u255E\n");          /* E2 95 9E */
    return 0;
}

How to Type It

Windows: Hold Alt and type 0198 on the numeric keypad, with Num Lock on. The leading zero picks the Windows code page. Alt+146, without the zero, types it too. No numeric keypad? In Word, type 00C6 and press Alt+X.
Mac: Press Option+Shift+'.
Linux: In GNOME, or any desktop running IBus, press Ctrl+Shift+U, type c6, then Space. With a Compose key set up, press Compose, A, E.
Phone: Tap Shift, then long-press A and pick Æ.

How to Type It

Windows: Hold Alt and type 198 on the numeric keypad, with no leading zero. US PCs insert ╞, but PCs set to code page 850, common in Western Europe, insert ã. No numeric keypad? In Word, type 255E and press Alt+X.
Mac: Press Control+Command+Space to open the Character Viewer, then search for "box drawings vertical single and right double".
Linux: In GNOME, or any desktop running IBus, press Ctrl+Shift+U, type 255e, then Space.
Phone: Phone keyboards have no key for it. Tap the character at the top of this page to copy it.

Frequently Asked Questions

Because the usual trick, NFKD followed by dropping non-ASCII, only works for letters that break down into a base letter plus an accent. Æ and ø have no decomposition, so both get deleted. Map them yourself first (Æ to AE, ø to o) or use a transliteration library: Python's unidecode turns Ærø into AEro.
Both, depending on the language. In Danish, Norwegian, Icelandic and Faroese it's a full letter with its own place in the alphabet, after Z in Danish and Norwegian. In English and Latin it's a ligature, so Æsop and Aesop, or encyclopædia and encyclopaedia, are the same word. Only the second group can swap it for ae without misspelling anything.
Same role, different letter. Danish and Norwegian write the sound with Æ and Ø, while Swedish and Finnish use Ä and Ö, so Bjørn and Björn are one name in two spellings. Unicode keeps them separate and no normalization links them, so a search across Nordic data has to fold Æ with Ä and Ø with Ö itself.
As AE. The machine-readable line of a passport follows ICAO rules that spell Æ as AE, with Ø becoming OE and Å becoming AA. Airline booking systems only take A to Z, so enter the name exactly as that line shows it, even though the printed name above it keeps the Æ.

ASCII 198

Uppercase AE ligatureBox T-junction pointing right, double horizontal

ASCII 198 is Æ on Windows and ╞ in old DOS.

Latin Letter

Box Drawing

#include <stdio.h>

int main(void) {

/* On Windows (code page 1252) byte 198 is Æ.

Modern terminals expect UTF-8, so print the code point, not the byte. */

printf("\u00C6\n"); /* UTF-8: C3 86 */

unsigned char b = 198; /* the raw Windows-1252 byte */

printf("%d 0x%02X\n", b, b); /* 198 0xC6 */

return 0;

}

#include <stdio.h>

int main(void) {

/* Byte 198 is ╞ only on a console using code page 437

(chcp 437 on Windows, or DOSBox). On a UTF-8 terminal the

lone byte 0xC6 is invalid and prints as garbage, often �. */

putchar(198);

/* char is signed on x86, so a plain char holding 0xC6 is -58.

Use unsigned char when you compare or index by byte value. */

char c = (char)198;

unsigned char u = 198;

printf("\n%d %d\n", c, u); /* -58 198 */

/* Portable: print the Unicode character as UTF-8 instead. */

printf("\u255E\n"); /* E2 95 9E */

return 0;

}