Upsilon (Υ or υ) is the 20th letter of the Greek alphabet.

Upsilon may also refer to:

• Latin upsilon (Ʊ or ʊ), a Latin letter
• Lake Upsilon
• Upsilon meson (ϒ)

See also[edit]

• near-close near-back rounded vowel, represented as ʊ (lowercase Latin upsilon)
• Ypsilon (disambiguation)
• Ipsilon (disambiguation)
• Upsilon Phi Delta
• Upsilon Phi Sigma
• Upsilon Pi Epsilon
• Upsilon Sigma Phi