Beta (upper case Β, lower case β) is the second letter of the Greek alphabet. It seems to have come from the Phoenician word "beth" that means "house" or "tent". The shape of B represented that thing itself (tent), the usual house of the Semites. In the Ancient Greek language, it was pronounced , but in Modern Greek is pronounced [v]. In the system of Greek numerals it has a value of 2. Beta should not be confused with a similar-looking but unrelated letter in German language orthography, ß, which denotes a long "s" sound.

Beta is the second highest caste in Aldous Huxley's dystopic satire Brave New World.

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

• The beta particle and beta decay in particle physics.
• The speed of an object relative to the speed of light (β = v/c) in special relativity theory.
• The voiced bilabial fricative (IPA) in phonology.

The Modern Greek name of the letter is /ˈviˑta/. The American pronunciation is /ˈbeɪtə/ whereas the British pronunciation is /ˈbiːtə/. See: American and British English differences, IPA

Letters that arose from Beta include the Roman B and the Cyrillic letters Be and Ve.

The Chinese radical Fu (阝) looks almost identical.