Statement of the problem. The ensemble is a type of collective musicmaking that dates back to ancient times and is an integral factor in the spiritual life of any nation. For Ukrainian culture, the traditions of the folk-instrumental ensemble have always been important, because they were associated with labor and ceremonial-ritual functions in society, people’s daily life, and secular forms of musical art. The article singles out significant elements of the process of academicization and chamberization of accordion ensembles in order to determine the characteristic features of Ukrainian folk-instrumental professionalism in ensemble music-making. In this context, the phenomenon of creative activity of “triple musicians” is highlighted, as a significant type of Ukrainian ensembleinstrumental performance. Special attention is paid to the crystallization of ensemble functions, and to the definition of the characteristic features of the Ukrainian harmonica and bayan culture. The bayan began to be introduced into European chamber-ensemble instrumental music only in the last decades of the 20th century; hence, the phenomenon of academization and chamberization of bayan ensembles is understudied, which determines the relevance of the research topic, prompting to make sense of their place in the general historical and stylistic process of ensemble music-making. The purpose of the article is to determine the characteristic features of Ukrainian folk-instrumental professionalism in the field of ensemble musicmaking, in order to popularize this type of performance in the Ukrainian national tradition. Recent research and publications. Relevant to the topic of the article is Yu. Loshkov’s work “Harmonica in Ukraine”, where “the specifics of harmonica performance in various spheres of domestic musical culture of the second half of the 19th and early 20th centuries” are determined (Loshkov, 2014: 238), and Igor and Liudmila Sniedkov’s article devoted to the Kharkiv bayan school (Sniedkov & Sniedkova, 2021), which contains information about the features of ensembles with the participation of the bayan. In M. Pliushchenko’s dissertation (2021) on timbretextural specificity of bayan and accordion transcriptions by Kharkiv composers of the late 20th – early 21st century, the parameters of Ukrainian instrumental and folklore professionalism are singled out. The scientific novelty of the presented study lies in emphasizing the role of folk-instrumental ensemble music-making in the historical-stylistic process and its peculiarities in Ukraine. Research results. The evolution of harmonica-bayan ensembles took place at first outside the traditions of classical chamber ensembles. The genesis of harmonica-bayan ensembles is closely related to the folk-instrumental tradition. In the aspect of the further movement of accordion ensembles towards academicization, as historically the first, such genetic and stylistic folklore features should be defined: the professionalism of instrumental ensembles since ancient times, which contributed to the further improvement of organological qualities and the development of ensemble playing; tendency towards individualization / differentiation of performers’ personalities (ensemble voices, in particular, in “triple musicians”); improvisational presentation of themes and theatricalization of musical communication. Conclusion. Collective musical performance has its roots in the ancient instrumental folk tradition. In the historical-stylistic process, genetically the first forms of collective music-making related closely to folklore instrumentalism were developed. With the obvious difference between folklore and academic types of music-making, there are also linked, tangential functions and properties of instruments. In the second half of the 20th century the bayan quickly assumed the position of both solo and ensemble status due to academicization and subsequent chamberization. These processes were related not only to folk instruments (bayan, domra, balalaika, bandura, whose classification as “folk” today does not correspond to the essence of their socio-cultural existence), but also to historically established accomplices of chamber-ensemble genres – violins, pianos, brass, percussions. And therefore, each new generation of musicians-performers on folk instruments has a need to research the mentioned tradition with the aim of further implementation of individual instrumental-folkloric segments into modern author’s compositions.