Epsilon (uppercase , lowercase  or lunate ; ) is the fifth letter of the Greek alphabet, corresponding phonetically to a close-mid front unrounded vowel . In the system of Greek numerals it has the value five. It was derived from the Phoenician letter He . Letters that arose from epsilon include the Roman E, Ë and Ɛ, and Cyrillic Е, È, Ё, Є and Э.

Epsilon (Ε, ε) is the fifth letter of the Greek alphabet.