In 1862, a volume of tales was published under the title Eredeti népmesék (‘Original Folktales’) by László Arany, the then 18-year-old son of János Arany, the national poet of the period. Eredeti népmesék has been classified by folkloristics as the first canonical folktale collection in Hungary. Besides scholarly recognition, it has also become one of the most popular folktale collections of the past one and a half century, as selected tales from this collection have been continuously republished in schoolbooks and anthologies and have become a regular element in children's literature. After the Second World War, in the basement of the main building of the Hungarian Academy of Sciences in Budapest, a huge pile of manuscripts had been found in very poor condition, consisting of, among others, various 19th-century folklore collections. In the 1960s, it was discovered that a part of these manuscripts was identical to the texts published in Eredeti népmesék. The vast majority of the manuscript tales had been recorded by the family members of János Arany, namely, his young daughter (Julianna Arany) and his wife (Julianna Ercsey), in the period between 1850 and 1862, presumably for family use. A comparison of the manuscript texts with their published versions revealed that in the editing process, László Arany significantly reworked the texts of the manuscript tales, implementing significant stylistic modifications. This article reports on the research project underlying the synoptic critical edition of the manuscript and published tales of the Arany family (2018). In the first part, the author presents the manuscript and published tales and their place in the history of Hungarian folkloristics, followed by an introduction of the members of the Arany family with an emphasis on their socio-cultural background, and concluding with a discussion of the roles they played in this collaborative folktale project as collectors, editors, copy editors, and theoreticians. The second part is a summary of the textological concept and techniques applied in the course of the development of the synoptic critical edition.