I is the ninth letter in the Latin alphabet, derived from the Greek iota (Ι, ι). It stood for the vowel /i/, the same as in the Etruscan alphabet. In Latin (as in Modern Greek) /j/ (as English Y in YOKE) was added. In Semitic, /j/ was the usual sound value of Jôd (probably originally a pictogram for an arm with hand), /i/ only in foreign words. In English, I represents different sounds, among them a diphthong that developed from /i:/ as well as short, open /I/ as in BILL. The dot over the lowercase 'i' is called a tittle.

India represents the letter I in the NATO phonetic alphabet.

In context, I is also:

• A word: the pronoun "I" that is used in the English language by a person to refer to himself or herself.
• In chemistry, a symbol for the chemical element iodine.
• In mathematics, the letter i is used for the imaginary unit, a complex number whose square is -1.
• In physics, the variable I for current. The imaginary unit is represented by j instead.
• A symbol (I) for the closed unit interval, that is all real numbers from 0 to 1 inclusive, and also for the identity matrix.
• The Roman numeral for one, whether uppercase or lowercase.
• A Swedish film made in 1966, see I.
• In the Turkish alphabet, "I" and "İ" are different letters.

Two-letter combinations starting with I:

• ia ib ic id ie if ig ih ii ij ik il im in io ip iq ir is it iu iv iw ix iy iz