The article discusses letters written by Philipp Segesser, a Jesuit priest serving as a missionary in Sonora, Mexico, to his family in Switzerland. Particular focus is given to the historical significance of the letters and to the process of transcribing and translating them for scholarly use. According to the author, the letters provide important information on Jesuit missions in the Sonora region as well as a glimpse into Segesser's personality and family life. Details related to Segesser's religious beliefs and his celebration of religious holidays are also presented. Other topics include Benito Crespo y Munroy, the Bishop of Durango, Mexico, and Segesser's attitude towards Indians. A translation of one of the letters, dated August 1, 1731, is also presented.