One can divide the development of the Bulgarian language into several periods.
- The Prehistoric period covers the time between the Slavonic migration to the eastern Balkans (c. 7th century CE) and the mission of Saints Cyril and Methodius to Great Moravia in the 860s.
- Old Bulgarian (9th to 11th centuries, also referred to as "Old Church Slavonic") – a literary norm of the early southern dialect of the Common Slavic language from which Bulgarian evolved. Saints Cyril and Methodius and their disciples used this norm when translating the Bible and other liturgical literature from Greek into Slavic.
- Middle Bulgarian (12th to 15th centuries) – a literary norm that evolved from the earlier Old Bulgarian, after major innovations occurred. A language of rich literary activity, it served as the official administration language of the Second Bulgarian Empire.
- Modern Bulgarian dates from the 16th century onwards, undergoing general grammar and syntax changes in the 18th and 19th centuries. Present-day written Bulgarian language was standardized on the basis of the 19th-century Bulgarian vernacular. The historical development of the Bulgarian language can be described as a transition from a highly synthetic language (Old Bulgarian) to a typical analytic language (Modern Bulgarian) with Middle Bulgarian as a midpoint in this transition.
Bulgarian was the first "Slavic" language attested in writing. As Slavic linguistic unity lasted into late antiquity, the oldest manuscripts initially referred to this language was as языкъ словяньскъ, "the Slavic language". In the Middle Bulgarian period this name was gradually replaced by the name языкъ блъгарьскъ, the "Bulgarian language". In some cases, this name was used not only with regard to the contemporary Middle Bulgarian language of the copyist but also to the period of Old Bulgarian. A most notable example of anachronism is the Service of Saint Cyril from Skopje (Скопски миней), a 13th-century Middle Bulgarian manuscript from northern Macedonia according to which St. Cyril preached with "Bulgarian" books among the Moravian Slavs. The first mention of the language as the "Bulgarian language" instead of the "Slavonic language" comes in the work of the Greek clergy of the Archbishopric of Ohrid in the 11th century, for example in the Greek hagiography of Clement of Ohrid by Theophylact of Ohrid (late 11th century).
During the Middle Bulgarian period, the language underwent dramatic changes, losing the Slavonic case system, but preserving the rich verb system (while the development was exactly the opposite in other Slavic languages) and developing a definite article. It was influenced by its non-Slavic neighbors in the Balkan language area (mostly grammatically) and later also by Turkish, which was the official language of the Ottoman Empire, in the form of the Ottoman Turkish language, mostly lexically. As a national revival occurred toward the end of the period of Ottoman rule (mostly during the 19th century), a modern Bulgarian literary language gradually emerged that drew heavily on Church Slavonic/Old Bulgarian (and to some extent on literary Russian, which had preserved many lexical items from Church Slavonic) and later reduced the number of Turkish and other Balkan loans. Today one difference between Bulgarian dialects in the country and literary spoken Bulgarian is the significant presence of Old Bulgarian words and even word forms in the latter. Russian loans are distinguished from Old Bulgarian ones on the basis of the presence of specifically Russian phonetic changes, as in оборот (turnover, rev), непонятен (incomprehensible), ядро (nucleus) and others. Many other loans from French, English and the classical languages have subsequently entered the language as well.
Modern Bulgarian was based essentially on the Eastern dialects of the language, but its pronunciation is in many respects a compromise between East and West Bulgarian (see especially the phonetic sections below). Following the efforts of some figures of the National awakening of Bulgaria (most notably Neofit Rilski and Ivan Bogorov), there had been many attempts to codify a standard Bulgarian language; however, there was much argument surrounding the choice of norms. Between 1835 and 1878 more than 25 proposals were put forward and "linguistic chaos" ensued. Eventually the eastern dialects prevailed,
and in 1899 the Bulgarian Ministry of Education officially codified a standard Bulgarian language based on the Drinov-Ivanchev orthography.