I (И и; italics: И и) is a letter used in almost all Cyrillic alphabets.
Because the Cyrillic letter І was derived from the Greek letter Eta (Η η), the Cyrillic ⟨И⟩ had the shape of ⟨H⟩ up to the 13th century.
The name of the Cyrillic letter І in the Early Cyrillic alphabet was ижє (iže), meaning "which".
In the Cyrillic numeral system, the Cyrillic letter І had a value of 8, corresponding to the Greek letter Eta.
In the Early Cyrillic alphabet there was little or no distinction between the letter ⟨И⟩ and the letter ⟨І⟩ which was derived from the Greek letter Iota (Ι ι). They both remained in the alphabetical repertoire because they represented different numbers in the Cyrillic numeral system, eight and ten.
Today they co-exist in Church Slavonic, with no pronunciation difference; and in Ukrainian, representing actual pronunciation differences. Other modern orthographies for Slavic languages eliminated one of the two letters in alphabet reforms of the 19th or 20th centuries: Russian, Macedonian, Serbian and Bulgarian languages use only ⟨И⟩, and Belarusian uses only ⟨І⟩.
Originally, Cyrillic ⟨И⟩ had the shape identical to the capital Greek letter Eta ⟨Η⟩. Later, the middle stroke was turned counterclockwise, resulting in the modern form resembling a mirrored capital Latin letter N ⟨N⟩ (this is why ⟨И⟩ is used in faux Cyrillic typography). But the style of the two letters is not fully identical: in roman fonts, ⟨И⟩ has heavier vertical strokes and serifs on all four corners, whereas ⟨N⟩ has a heavier diagonal stroke and lacks a serif on the bottom-right corner.
In roman and oblique fonts, the lowercase letter ⟨и⟩ has the same shape as the uppercase letter ⟨И⟩. In italic fonts, the lowercase letter ⟨И⟩ looks like the italic form of the lowercase Latin U ⟨u⟩. Both capital and small hand-written forms of the Cyrillic letter I look like hand-written forms of the Latin letter U.
Since the 1930s, ⟨и⟩ has been the tenth letter of the Russian alphabet, and in Russian, it represents /i/, like the i in machine except after some consonants (see below). In Russian, it typically denotes a preceding soft consonant and, therefore, is considered the soft counterpart to ⟨ы⟩ (which represents [ɨ]) but, unlike other "soft" vowels (⟨е⟩, ⟨ё⟩, ⟨ю⟩ and ⟨я⟩), ⟨и⟩ in isolation is not preceded by the /j/ semivowel. In Russian, the letter has been seen combined in the digraph ⟨ио⟩ (as were ⟨ьо⟩, ⟨їô⟩ and ⟨iо⟩) to represent ⟨ё⟩ before its existence around 1783. There still exist some apparent confusion in the transcription of some foreign words.
⟨И⟩ pronounced as [ɨ] in ⟨жи⟩ (sounds like ⟨жы⟩ [ʐɨ]), ⟨ши⟩ (sounds like ⟨шы⟩ [ʂɨ]) and ⟨ци⟩ (sounds like ⟨цы⟩ [t͡sɨ]), because in Russian, the sound [i] is inarticulable after "zh" ⟨ж⟩, "sh" ⟨ш⟩ and "ts" ⟨ц⟩.
In the Bulgarian Cyrillic alphabet ⟨и⟩ is the ninth letter, representing the sound /i/. It also occurs with a grave accent, ѝ, in order to distinguish orthographically the conjunction ⟨и⟩ ('and') and the short form of the indirect object ⟨ѝ⟩ ('her').
In Kazakh, ⟨И⟩ is used for /əj/ and /ɪj/ in native words and for /i/ in loanwords, while ⟨І⟩ is used for /ɪ/ in native words.
The letter ⟨И⟩ is the eleventh letter of the Ukrainian alphabet and it represents sound [ɪ], which is a separate phoneme in Ukrainian. The Ukrainian ⟨и⟩ can be transliterated to other languages using Cyrillic script by both ⟨и⟩ and ⟨ы⟩, due to lack of common transliteration rule. Speakers of other Slavic languages can perceive Ukrainian [ɪ] as either [i], [ɨ] or sometimes even [e] (see Ukrainian phonology for more on pronunciation of [ɪ]). The sound [i] in Ukrainian is represented by letter ⟨і⟩, the same as in Belarusian.
In the Serbian Cyrillic alphabet, ⟨и⟩ is the tenth letter of the alphabet. In Serbian, it represents /i/, like the i in machine or i in bill. In the Latin Serbian alphabet, the same vowel is represented by "I/i".
In Macedonian, it is the eleventh letter of the alphabet and represents the sound /i/.
The vowel represented by ⟨и⟩, as well as almost any other Slavonic vowel, can be stressed or unstressed. Stressed variants are sometimes (in special texts, like dictionaries, or to prevent ambiguity) graphically marked by acute, grave, double grave or circumflex accent marks.
Special Serbian texts also use ⟨и⟩ with a macron to represent long unstressed variant of the sound. Serbian ⟨и⟩ with a circumflex can be unstressed as well; then, it represents the genitive case of plural forms to distinguish them from other similar forms.
Modern Church Slavonic orthography uses the smooth breathing sign (Greek and Church Slavonic: psili, Latin: spiritus lenis) above the initial vowels (just for tradition, as there is no difference in pronunciation). It can be combined with acute or grave accents, if necessary.
⟨И⟩ with a breve forms the letter ⟨й⟩ for the consonant /j/ or a similar semivowel, like the y in English "yes." The form has been used regularly in Church Slavonic since the 16th century, but it officially became a separate letter of alphabet much later (in Russian, only in 1918). The original name of ⟨й⟩ was I s kratkoy ('I with the short [line]'), later I kratkoye ('short I') in Russian. It is known similarly as I kratko in Bulgarian but as Yot in Ukrainian.