A subject-matter of the present edition is correspondence between an eminent historian - Jan Ptasnik - and Czech historian - Jaroslav Bidlo. The published letters significantly enrich the knowledge of connections and relationships of Czech and Polish intellectuals in the beginning of the 20th century. Among others, they reveal an attitude of Jan Ptasnik both towards southern neighbours of Poland and some historiographic matters at issue. The letters of Ptasnik are kept among posthumous works of Bidlo in Record Office of Academy of Sciences of Czech Republic in Prague. However, a few of Bidlo's replies are kept in Manuscripts' Section in National Library.