The Balkan sprachbund or Balkan language area is the ensemble of areal features—similarities in grammar, syntax, vocabulary and phonology—among the languages of the Balkans. Several features are found across these languages though not all need apply to every single language. The languages in question may be wholly unrelated, belonging to various branches of Indo-European (such as Slavic, Greek, Romance, Albanian and Indo-Aryan) or even outside of Indo-European (such as Turkish). Some of the languages use these features for their standard language (i.e. those whose homeland lies almost entirely within the region) whilst other populations to whom the land is not a cultural pivot (as they have wider communities outside of it) may still adopt the features for their local register; this in turn is viewed as non-standard by their respective peoples away from the region.
While they share little vocabulary, their grammars have very extensive similarities; for example they have similar case systems and verb conjugation systems and have all become more analytic, although to differing degrees.
The earliest scholar to notice the similarities between Balkan languages belonging to different families was the Slovenian scholar Jernej Kopitar in 1829.August Schleicher (1850) more explicitly developed the concept of areal relationships as opposed to genetic ones, and Franc Miklošič (1861) studied the relationships of Balkan Slavic and Romance more extensively.
Nikolai Trubetzkoy (1923),Kristian Sandfeld-Jensen (1930), and Gustav Weigand (1925) developed the theory in the 1920s and 1930s.