Correspondence of Croatian composer and music writer Antun Dobronić is being kept, for the most part, in the Music Collection of the National and University Library in Zagreb. This master’s thesis is the result of listing and analyzing 792 units of this collection relating to the time period between 1887 and 1929. The data was organized in a Microsoft Excel table as a catalogue and was then analyzed. Based on the contents of the letters, eight thematic units were created: youth in Dalmatia, Dobronić’s work as a composer, work as publicist, his contribution to the Cecilian movement, aspiration to write a music history piece in Croatian, correspondence with Croatian and foreign music publishers, taking part in the organization of the International exhibition Musik im Leben der Völker in Frankfurt in 1927, and the state of Croatian music in World War I. By contextualizing the data from the letters based on relevant works cited, these thematic units were transformed into case studies. The research results confirmed the already existing data regarding the life of Antun Dobronić while offering some new points of view for some of them, as well as providing some little-known facts, such as his work on a book on music history or the scope of his involvement in the organization of International music festival in Frankfurt.