The project seeks to reconsider the place of the Grand Duchy of Lithuania within the confessional geography of early modern Europe through an examination of communication channels between the Grand Duchy of Lithuania and the countries of Western and Central Europe during the age of confessionalisation (ca 1550s – 1660s). All previous studies on the place of Eastern European states in the European Reformation movement have presented Poland-Lithuania as a marginal region and emphasised the Roman Catholic or Eastern Orthodox dimension of the Grand Duchy of Lithuania. The project offers a different perspective based on the premise that the Grand Duchy of Lithuania played a conspicuous role within the international Protestant camp. The main hypothesis of the proposed research is the argument that after the Union of Lublin the Grand Duchy of Lithuania managed to form its own peculiar, Protestant – rather than Catholic or Orthodox – identity in the perception of Western Europeans in contradistinction to the Catholic identity of the Kingdom of Poland.