U is the twenty-first letter of the modern Latin alphabet.

U was originally a capital letter like J and it was only Pierre de la Ramée who made the distinction between capital and small letter. See V.

Uniform represents the letter U in the NATO phonetic alphabet.

U is also:

• In chemistry, the symbol for uranium
• British novelist Nancy Mitford brought to popular attention the linguistic terminology "U" and "non-U" to indicate the speech markers of upper class and non-upper class British speakers respectively.
• short for "you", used in SMS or instant messages.
• In computer science, 1 U (= 44 mm or 1¾ inch) is the unit of the height of computer chassis, also called a rack unit.
• In mathematics, stands for union, the upside-down stands for intersection (both are operators for sets)

Two-letter combinations starting with U:

• ua ub uc ud ue uf ug uh ui uj uk ul um un uo up uq ur us ut uu uv uw ux uy uz