ENThe article analyzes contemporary publishing instructions and methodological recommendations for the publication of Cyrillic sources formulated in Russian, Belarusian and Ukrainian editing, as well as selected source publications of Cyrillic documents from the territory of the Grand Duchy of Lithuania from the 16th-17th centuries. The indicated publications will be analyzed from the point of view of the general assumptions of rendering the text of the published source, as well as specific solutions on how to render in the text of the edition the letters used in the original document. As the analysis shows, Russian, Ukrainian and Belarusian editorial theory lacks universally accepted theoretical assumptions when publishing Cyrillic sources from the early modern period. These assumptions range from radical proposals to render the text of the source as close as possible to the graphics and orthography of the original to proposals for its limited modernization. Moreover, the assumptions of some of the recommendations under consideration are complex and not always transparent. Most of the publishers of the analyzed editions do not apply the solution of strict rendering of the graphics and orthography of the text, making its more or less limited modernization, although exceptions to this rule are encountered. In terms of the way of rendering letters that have fallen out of use, one can see the existence of three groups of issues: those that by most of the theory and practice are resolved in a uniform way (such as the issue of rendering the digraph “кг” in the text), those for which, as a rule, two solutions are encountered: rendering a given letter or replacing it with an equivalent from the modern Cyrillic alphabet, and those that are characterized by a wide range of possible and encountered solutions.To the last group belong the issues of rendering the letters “ѣ” and “є” and the character “ ' ” in the text. The analysis carried out allowed the publishers to formulate their own solutions, which are the resultant of two tendencies: to take into account in one edition the peculiarities of the texts in two languages, and at the same time to unify the publishing rules. These solutions are presented in the form of proposals for publishers of subsequent analogous source editions. With regard to the way of rendering the letters used in the source text, which have fallen out of use in modern East Slavic languages, it has been proposed to render them using the letters used today, to leave the digraph “кг” in the edition, and to consistently render the sign “ ' ” as “и”. Key words: source editing, publishing principles, cyrillic sources, sejmik records, Grand Duchy of Lithuania, Vilnius voivodship. [From the publication]