The connections between the Polish Reformed Churches and the Dutch Eglises Wallonnes have never been properly examined. Apart from a few notes in articles from the beginning of the twentieth century, no attempt has been made to describe them in an integrated manner, taking into account the Walloon archives in the Bibliotheque Wallonne, as well as other Walloon sources. The aim of this publication is to examine Walloon–Polish communications in the eighteenth century, a time important for both the Walloons and the Polish Reformed. While for the former it was a period of growth and expansion, for the latter it was quite the opposite. This difference allowed the Walloon to help the Poles in their plight, strengthening the Walloon's position as supporters of endangered Protestant communities worldwide.