These two collections of Yiddish letters date from the second half of the 17th century and are being published here in full for the first time. The opening five-letter collection was archived together with extensive information about three Jews from Hamburg-Altona, who had been arrested and investigated in Copenhagen in August 1666. The second collection consists of eighteen letters exchanged between Hamburg-Altona and Copenhagen in January 1678. They concern the family and business affairs of a range of people, among them some of Glikl Hamel’s relatives, business associates and acquaintances. Together, the two collections provide a wealth of illuminating new details about the economic, cultural, social, and family life of early modern Ashkenazi Jews in Northern Europe, and also shed light on the practice of Yiddish letter-writing at the time. The English section consists of an introduction followed by a synopsis of each letter, while the Hebrew section comprises a transcription of the original texts as well as their facsimile images.