Harfa duchowna (1585), a prayer book compiled by Marcin Laterna, a Jesuit, was probably the most successful post-Tridentine Polish bestseller. However, it has never been explored thoroughly, and not at all as a post-Tridentine printed book. The paper shows Harfa at the backdrop of sixteenth- and seventeenth-century Catholic prayer books in Poland and defines its key role as a model for later publications of this kind. The form of the book is analysed in connection with its content and broader cultural context, implying that successful counter-reforming of devotional publications had to be done on the level of content as well as form. The connections between Kraków and Antwerp printing, clearly visible in the woodcuts used in Harfa by its printers, are mentioned and the information about the number of editions and existing copies is also included.