Ø (and ø) is a Scandinavian vowel letter.

The letter Ø or the symbol ∅ (a circle crossed by a diagonal slash) etc. may also refer to:

• Close-mid front rounded vowel (IPA: ø)
• Zero (linguistics) (∅)
• Berber Academy yah (ⵁ), a Tifinagh letter, corresponding to "h"

• Slashed zero (0︀), U+0030 U+FE00 in Unicode, a representation of the digit 0 (zero) to distinguish it from the letter O
• Slashed letter 'O' (O̸), a representation of the letter O to distinguish it from the digit 0 (zero)
• The symbol for diameter (⌀), U+2300 in Unicode
• The symbol to represent a phenyl group
• The symbol for the empty set ( or as a character) in mathematical set theory, U+2205 in Unicode

• Ø, Denmark, a piece of land in Jutland, Denmark
• Half-diminished seventh chord (^ø), in music
• Ø, the solo identity of Finnish musician Mika Vainio of electronic music band Pan Sonic
• Ø, the 2021 EP by British alt-rock band Blood Red Shoes

• Circled division slash (⊘), U+2298 in Unicode

• Voiceless bilabial fricative (IPA: ɸ)
• Phi (Φ and φ), a Greek letter, corresponding to "f" or "ph"
  • Several uses of phi as a symbol for angles, etc.
• Ef (Cyrillic) (Ф and ф), a Cyrillic letter, corresponding to "f" or "ph"

• Yah (ⵀ), a Tifinagh letter, corresponding to "h" or "b"

• Voiceless dental fricative (IPA: θ)
• Theta (Θ and θ), a Greek letter, corresponding to "th"
• Theta nigrum (ꝋ) for "obiit" ="died"
• Fita (Ѳ and ѳ), an Old Cyrillic letter, corresponding to "f" and transliterating Greek theta
• Oe (Cyrillic) (Ө and ө), Cyrillic barred O, representing an open-mid front rounded vowel in some Turkic and Mongolic languages
• Yab (ⴱ), a Tifinagh letter, corresponding to "b"
• Load line mark (⦵), showing the maximum draft of a ship
• Standard state (⦵), in chemistry

• Circle symbol (disambiguation)
• Null (disambiguation)
• Null symbol (disambiguation)
• Barred O (disambiguation)
• 0 (disambiguation)