Alpha (uppercase Α, lowercase α) is the first letter of the Greek alphabet. In the system of Greek numerals it has a value of 1.

The lower-case letter α is used as the symbol for:

• Angular acceleration in physics.
• The alpha particle and alpha decay in physics.

Alpha is also the highest and most intelligent caste in Aldous Huxley's dystopic satire Brave New World.

Alpha is often used as an adjective to indicate the first or most significant occurrence of something, as in alpha male or alpha version.

Letters that arose from Alpha include the Roman A and the Cyrillic letter A.