Serbian, Croatian and Bosnian are closely related, mutually intelligible Southern Slavonic languages formerly known collectively as Serbo-Croat. They have about 18.5 million speakers, mainly in Serbia, Croatia, Bosnia and Herzegovina and Montenegro.
The division between Croats and Serbs originates in the 11th century, when both groups converted to Christianity. The Serbs aligned themselves with Constantinople and the Eastern Orthodox church and adopted the Cyrillic alphabet though also use the Latin alphabet, while the Croats favoured the Roman Catholic church and the Glagolitic alphabet. The Latin alphabet was gradually adopted by the Croats, though they continued to use Glagolitic for religious writings until the 19th century. After the Turkish conquest of Serbia and Bosnia, Islam spread to parts of Bosnia and the Arabic script was sometimes used.
Today Croatian is written with the Latin alphabet, Serbian is written mainly with the Cyrillic alphabet, though the Latin alphabet is sometimes used, and Bosnian uses both alphabets.