The Teutonic Order in Prussia recognised and acknowledged its responsibility to catechise both the German-speaking colonists and the native population. The Reformation made no radical changes to these requirements, but gave them serious attention. During the 1540s to the 1560s, several Catechisms for the non-German subjects of the Duke of Prussia were prepared and published in Königsberg, including three in the Old Prussian language. The editor of the first and second Old Prussian-language Catechisms published bilingual books, with the German Catechism on the left-hand page, and the same text on the right-hand page in the Old Prussian language. Reinhold Trautmann established that the source of the Decalogue in these books was Luther’s 1531 Small Catechism. However, he had difficulties confirming the sources of the remaining four parts of the Catechism, since he found a number of words and phrases which could not be identified as coming from Luther’s Catechisms. The article elaborates on Trautmann’s thesis that the source of the German Decalogue is Luther’s 1531 Enchiridion. In addition, it argues that the sources of the remaining parts of the Catechism were German-language catechetical and liturgical texts that were circulating in Prussia at that time.