Bulgarian is an Indo-European language, a member of the South branch of the Slavic languages, along with Serbo-Croatian, and Slovenian.

Bulgarian is the most widely spoken language in Bulgaria. It is also spoken in Canada, Greece, Hungary, Israel, Macedonia, Moldova, Romania, Serbia, Turkey, Ukraine and the United States, with an estimated total of 9 million native speakers.

Bulgarian is the oldest written Slavic language. Historically it is divided into Old Bulgarian (9th to 11th century), Middle Bulgarian (12th to 15th century) and Modern Bulgarian (16th century onwards); the present-day written language was standardized in the 19th century. Some words and structures remain from the language of the Bulgars, the Central Asian people who moved into present-day Bulgaria and eventually adopted the local Slavic language. The Bulgar was otherwise unrelated to Bulgarian.

Bulgarian demonstrates several linguistic innovations that set it apart from other Slavic languages, such as the elimination of noun declension, the development of a suffix definite article (possibly inherited from the Bulgar language, or taken from Albanian), the lack of verb infinitive, and the retention and further development of the Proto-Slavic verb system. There are various verb forms to express non-witnessed, retold, and doubtful action.