The Serbian Cyrillic alphabet (Serbian: Српска ћирилица / Srpska ćirilica, IPA: [sr̩̂pskaː t͡ɕirǐlitsa]), also known as the Serbian script, (Српско писмо, Srpsko pismo, Serbian pronunciation: [sr̩̂psko pǐːsmo]), is a standardized variation of the Cyrillic script used to write Serbo-Croatian, namely its Serbian and Bosnian (mainly in Republika Srpska) standard varieties. It originated in medieval Serbia and was significantly reformed in the 19th century by the Serbian philologist and linguist Vuk Karadžić.
The Serbian Cyrillic alphabet is one of the two official scripts used to write modern standard Serbian, the other being Gaj's Latin alphabet. Karadžić based his reform on the earlier 18th-century Slavonic-Serbian script. Following the principle of "write as you speak and read as it is written" (piši kao što govoriš, čitaj kao što je napisano), he removed obsolete letters, eliminated redundant representations of iotated vowels, and introduced the letter ⟨J⟩ from the Latin script. He also created new letters for sounds unique to Serbian phonology. Around the same time, Ljudevit Gaj led the standardization of the Latin script for use in western South Slavic languages, applying similar phonemic principles.
