Stoyko Stoykov in the context of "Nestram-Kostenar dialect"

The Kostur dialect (Macedonian: Костурски дијалект, Kosturski dijalekt) is a member of the Southwestern subgroup of the Southeastern group of dialects of the Macedonian language. This dialect is mainly spoken in and around the town of Kastoria, known locally in Macedonian as Kostur, and in the surrounding Korešta region, (Macedonian: Корешта; in the Kostur dialect: Korèshcha/Корèшча) which encompasses most of the area to the northwest of the town. The Kostur dialect is also partially spoken in Albania, most notably in Bilisht and the village of Vërnik (Vrabnik). The dialect is partially preserved among the ″people of Bulgarian origin in Mustafapaşa and Cemilköy, Turkey, descending from the village of Agios Antonios (Zhèrveni) in Kostur region (Aegean Macedonia)″.

The Kostur dialect shares strong similarities with the Nestram-Kostenar dialect and the Korča dialect. Bulgarian linguist Stoyko Stoykov regarded the Nestram dialect as a subgroup of the Kostur dialect, part of Bulgarian dialects. Other Bulgarian linguists also regard the dialect as a Bulgarian dialect.

Bulgarian dialects are the regional varieties of the Bulgarian language, a South Slavic language. Bulgarian dialectology dates to the 1830s and the pioneering work of Neofit Rilski, Bolgarska gramatika (published 1835 in Kragujevac, Principality of Serbia). Other notable researchers in this field include Marin Drinov, Konstantin Josef Jireček, Lyubomir Miletich, Aleksandar Teodorov-Balan, Stoyko Stoykov.

The dialects of Macedonian are classified as part of Bulgarian in the older literature. Presently, Bulgarian linguistics continue to treat it as such.Since the second half of the 20th century, foreign authors have mostly adopted the convention of treating these in terms of a separate Macedonian language, following the codification of Macedonian as the literary standard language of Yugoslav Macedonia. However, some contemporary linguists still consider Macedonian as a dialect of Bulgarian. Macedonian authors in turn tend to treat all dialects spoken in the geographical region of Macedonia as Macedonian, including those spoken in Bulgarian Macedonia. Together with their closest lexical and grammatical relative they comprise the Eastern South Slavic branch. The present article treats all these dialects together, because of their close structural similarity and the fact that many important dialect boundaries intersect both territories.