The essay uses Ukrainian immigration in the USA to demonstrate the significance of periodicals (mainly newspapers) for historical research. Although it represents a frequently ignored resource, it serves as a truly basic source of information in many cases. Research into periodicals published by Ukrainian expatriates (mostly in the interwar period) demonstrates the composition and ideological focus of the community and problems of its everyday life. Description of individual issues allows definition of the publishing activity within the Ukrainian diaspora in the USA and its obstructions. The essay is particularly dedicated to periodicals published in the interwar period which are deposited in the Prague Slavonic Library. The library took the collection over after 1945 when the Russian Foreign Historical Institute was liquidated. The essay demonstrates the outstanding significance of the collection on examples of concrete issues deposited in the Slavonic Library (many of the issues are not available in any American library) and it analyses their contents. Simultaneously, it sums up the composition of the preserved collection and hints at world rarities in an accompanying catalogue.